I think you want to plug your bass into the amp, and get an XLR cable to run from the amp into the Focusrite XLR input.
This will allow you to play your bass thru the amp and record a balanced signal to the focusrite.
Two ways you can do this.
If you have effects or pedalboard, you can plug the bass into the pedals, and the pedals to the amp.
This way, when you send the signal to the DAI, you will send the sound you created from the effects.
Or
If you rather, you can plug the bass into the amp, and the Xlr from the amp to the DAI, and plug your effects inot the FX loop (if you have one) and then you can mix your effects with your dry signal, and have the sound you create from your pedals to play thru the amp, BUT the signal from the amp to the DAI will be ONLY the bass signal, and you can mix the effects into the bass track.
If you are trying to acheive a different then standard set up, I am not certain I understand what you are trying to do and may require a little more info.
Also, if you do this, you can also use your headphones from the DAI and hear only your bass, OR a headphones from the amp to hear the WET sound, if you require headphones while playing.
Also, I am no where near an expert in this matter, so you may get better answers from others on the forum.