I would recommend a Pod X3. You can biamp a bass amp with a guitar amp. My preference is a GK sim for the low end and a gnarly Diezel Herbert for the upper mid and high drive.
Is there any further information about the Darkglass preamp? Nolly mentioned in a video that its midrange would be more nasal than usual. Personally I would say that there will be similarities with the EQ of the B7K. A more nasal midrange around 800 Hz (I think 1k in the B7K?) combined with...
I'm a Thumb guy, therefore i'd say go Thumb. But the FNA is also a very nice bass.
Very important: If you do not like the Thumb tone, don't get it, 'cause it will always be there, no matter how you EQ.