Did you knew you could also bypass your amp’s preamp by using a (preamp) pedal that goes into your return?
So for example on my old head I was using my BDI21 as my preamp and only used the head to power the cabs.
The customer service from DG is usually very good. I mean Doug himself takes his time to reply on the Talkbass forums. 
FYI- Darkglass just responded to me:
I had a few questions about the M500v2 amp.
When I look at the block diagram for it, I don’t see where the Effects Loop is mentioned. Can you please let me know where this fits in the diagram? RESPONSE: The effects loop is marked as “pre-out, power in” in the block diagram.
Would I be able to send the signal into another amplifier using the effects out or another method? RESPONSE: Yes, the effects send can be used to split the signal into another amp.
The block diagram makes it look like the Aux-In is only for the headphone out. i.e. It won’t play through the speaker out. Is that true? RESPONSE: True, the AUX IN is routed only into the headphone out.
Assuming I can send the signal into another amplifier, it would be good to know if this includes the Aux-In or not. RESPONSE: The signal from the effects send will not have the AUX IN signal in it.
Here’s the block diagram again:
Pretty much as we thought, it sounds.
So… are you gonna buy it? 
I don’t know…
Currently torn between three different paths (there are infinitely more, but I’ve narrowed it down to these three):
Get a new combo and a Zoom B3n to tide me over for a bit until I figure out what I really want. Effectively using the B3n as a gap filler.
Get a new combo and the MK500v2 and plan on taking that with me to gigs to use as my “pedalboard”, even if using the cabinet/amp there. I’m OK with this, but I know it’s a bit unusual. Idea would be to use the Aux-In on the combo (at home) to play along with backing tracks.
Get a MK500v2 and a Cabinet. Though this one doesn’t really work well for me without the addition of something else as the Aux In is only for Headphones unfortunately. But I could add something like the Darkglass Element to the effects loop.
For the Combo I’m leaning towards the new Ampeg Rocket Bass Amps. Either the RB-112 or the RB-115. Both are 100w internal speakers. The 115 also supports 100w externally to a cabinet. For the cabinet, I’ve not really looked into that very much, but there is a company here in the UK called Barefaced that everyone raves about, so have been looking into those.
Aiming to make a purchase on Monday so at the home stretch now.
I would say think a little about what genres you want to play and the sound you are looking for. Maybe that will make your decision easier? Good luck 
Maybe think about combining this idea, but get the Zoom B1-four instead of the B3n.
You can maybe go for a little cheaper cabinet, like if you are thinking $400 for a cabinet, maybe limit it to $325. Use the money saved to add the Zoom B1-four to the mix.
This way you get your Aux in, and you get the head you want, plus you get the multi fx to LEARN what you like. You can easily get $50-$60 for a used B1-Four, so you can just keep it as long as you are in the learning phase.
You will get to see if the Head works for you as a Pedalboard in every situation you need it for. If not, you have the Zoom Multi-FX processor to play with and see if, 1 - the Zoom and the MK500v2 are ENOUGH FX for you, or if you may decide to add a few modulation pedals and get rid of the Zoom when you do.
You will only need to bring the Head and Zoom to the rehearsal or gig, BUT when you go home, you will play thru the same set up (Bass to Zoom To MK500v2 To Cabinet) so it will stay consistent with what you do at gigs or rehearsal. Bass to Zoom to Head to Cab.
I realize the B3n is more of an investment, and in the end, may give you better performance if you really use alot of FX and Amp and Cab sims in the same chain you create. The Zoom B1-four and the pedal MS-60b I THINK have a little less processing power (maybe alot) then the B3n, but it doesn’t sound like you are going to max out the Multi FX with 5 pedals and an amp sim and cab sim in a single slot. FWIU, when you max everything out, you may experience problems with processing, and IDK how to say it in audio terms, but it would be like pixelation on a tv when the blu-ray or DVD can’t process all the stream correctly in the same time.
But again, I don’t think you will use the Multi FX like this. I think the Zoom B1-four will be plenty for you. Of course, I base this thought only from what I have read you write in this thread. If you do want to go crazy with pedals and totally changing your tone and sound altogether, with synthesizers and modulation, then yeah, I think you MAY need the B3n (but somebody else should verify this), but if you just want to add a little delay and reverb, maybe compression, you will be fine with the Zoom B1-four. I never had any issues when playing with it, and I loaded it up pretty heavy at times, but I was not using the Amp and Cab sims at the same time. I have heard those suck the most of the processing power.
Just a thought, but I think it gives you alot of the options you want, and it keeps you in a cabinet at home, which could help you to create your sound and more easily replicate it when you go play away from home.
If it ever comes down to it, taking a modern cabinet with you to a gig most likely will be easier to move around than a combo amp, as they are often lighter than combo amps. Plus this is not really the norm, it will only be if you go play a backyard party or something and there is no equipment and limited power and you have to take your cabinet. Otherwise, you will be set.
I’d agree. The B1four is a great buy. The biggest advantage of the B3n is the much better user interface for stompbox mode, but I think this would only be a factor for you for power usage. I don’t see you running large effects chains.
On the other hand, the B1four has the same amp and cab sims, same effects, and just can’t run as many at the same time. It’s plastic but it is really durable plastic. I dropped a B1on once and it was unharmed, and dented the floor. Zoom build quality is good.
Alternative you could buy a preamp with an aux-in and use that pre-amp for practice and home? For example DG preamps have an aux-in and so does GK Plex. By using the fx loop you could even skip the preamp of your head/combo amp. Just an idea 
