I would still avoid sending to the amp from the DAI and sending to the DAI from the amp. I’m guessing you’ll get a horrible feedback loop if it works at all.
pretty much like that 
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To be clear, I don’t think the idea of feeding the output of your DAI back in to your bass amp is a super good plan at all. If you are going to do it, you should probably do it through the normal input, but then you should NOT send the output from the bass amp back to the DAI. In general you want the signal flows to/from an amp to be unidirectional.
I’d recommend:
Bass into the amp
Amp into the DAI via its DI out
DAI output to computer via USB
DAI sound output to monitor speakers
If you must use the bass amp for outputting everything, then avoid sending its signal back to the DAI and consider just sending the DAI line out to the bass amp input (the normal one, not effect return). But I don’t recommend this for several reasons.
I send the output of my DAI to an amp, but it is my headphone amp, so it’s much closer to the “monitor speaker” scenario I recommend above.
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I agree with @howard, this is correct and good advice.
In the diagram I posted of my DAI setup, although I have an output from the DAI going back to the amp, this is only able to be be used when just listening to the amp, never when recording (as I said in posts above). I use this aux signal going back to the amp to play backing tracks into the amp, or the B2B audio when learning. But when I’m practicing, I’m not using the the XLR line output from the amp back to the DAI (which is now messed up being a combined signal). I disable it in the DAI control software so there is no feedback loop.
@howard is right, and on the setup I posted, when I come to record I would need to use headphones or monitor speakers to play the backing track, and not send it to the amp.
That’s why on the diagram I posted I labelled monitor speakers as a future purchase.
(Perhaps in hindsight on the diagram I posted I should have made a note about when the aux signal back to the amp can and can’t be used, and that proper operation of the setup relies on the Focusrite Control software being setup for various configs like practicing, recording etc)
EDIT:
All the above is still true but there is a workaround I think :
I think @PamPurrs way of connecting the Rumble back the DAI is the way to go, if I understand @PamPurrs setup properly. Rather than what I’ve done, which is use the XLR line output from the Rumble back to DAI, if I use the FX_Send output instead, then this is after the amp pre-amp, but BEFORE the Aux in signal gets mixed to the output. This should allow the Rumble to be used as a monitor for the backing track even when recording, but feed just the guitar signal back to the DAI. I need to give it a go.
EDIT 2:
I have tried using the Rumble’s FX_Send instead of the main XLR line output , and it works ok.
You can send bass output, plus aux signal to the Rumble, monitor both on the one amp (saving having to use headphones or buy separate monitors), and you still get a bass only signal in the Scarlett (to use in a DAW) via the FX_Send, and a separate aux backing track. I’m going to amend the diagram I posted above and post a new version.
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Here is a revised version of my Scarlett setup with the changes mentioned above to use the Rumble FX_Send.
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Thanks @PamPurrs.
I’m happier with it now, I don’t like wearing headphones, and wasn’t too keen to pay out for separate monitor speakers, so this config allows recording with a bass signal not mixed with backing track, and monitoring of both the bass and backing track audio via the Rumble.
Your approach to use the FX_Send out of the Rumble is a good one.
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For this version to work, people also have to make sure they don’t send their bass signal back out the DAI and into the aux input, or else it could flange against the bass signal already running through the 100 depending on delays.
I saw @Lanny 's note about the “Beginner” thread morphing into advanced and being too much for a beginner to read through. Maybe there’s some kind of thread splitting that can happen here @JoshFossgreen?
I really appreciate @Mark_UK, @howard and @PamPurrs working through all the details of an advanced setup.
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Yeah, like Recording Hardware “Advanced” setup?
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Yes agreed, hence my comment on the DAI box that you have to get the control software set up for your scenario. Cheers.
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I’m really not sure what I have is an advanced set up! 
Just one interface, amp, bass and pedals in the main. If you have an interface then you also have a PC/laptop.
The diagram probably looks complicated as I thought I would label all the I/O fully in case it was a help to anyone.
You can remove from my setup the additional tablet I use, and DAC. It’s on there just as an example of what I did, not a recommendation.
The pedal board (if my mini setup can be called that!) is just on the diagram for completeness. I could have just shown the bass going into the amp directly.
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I think you and Pam are right on the edge of the most functionality you could possibly squeeze out of a DAI! Ironically, it gets easier the more equipment one has.
I think when learning this all for the first time it’s difficult for people to wrap their head around the things they can’t see, what happens inside the 100 and how to set up the DAW/DAI monitoring/routing for different scenarios.
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Hi Mark
why not connecting connecting the XLR form the rumble instead of the FX send?
You will make use of the cab sim,so you get the “rumble” sound
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Yeah, plus the ground lift if needed (and you never know until you need it.)
I wouldn’t use the FX loop for this myself.
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I tried that and all I get is a loud, unbearable screeching noise the moment I switch on the amp. The FX send is the only way to go.
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did you connect that aux cable as well?
You should not feed your amp signal back into the amp through a DAI
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That’s because you have a feedback loop, because you are trying to send the DAI output as input to the amp, and the amp output back in to the DAI as input. Don’t do that
The bigger question is why you don’t have a feedback loop using the effects loop. You might just be be lucky. But the fundamental problem is the circular signal path, not the XLR out per se.
^^ exactly
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Nope…
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I don’t understand, what’s so bad about plugging the bass and drum machine, etc into the DAI and the DAI into the input of the amp? It seems to work fine.
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It’s because the aux input gets mixed into the XLR out. The FX send is bass only with no aux mixed in so there’s no chance to make a DAW setting that would cause a feedback loop.
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Ahh! Yeah, that makes sense. Mystery solved.
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