I have used pretty much 95% of the guitar amps in each of the units with9 bass. The key is to pair the amp model with a compatible bass cab IR. That's one reason I started Dr Bonkers, because no one at the time was approaching the units from that perspective.
There are 6 or 8 bass amps in the unit too.
Most of the modulation, drive, and delay blocks have a low cut and hi cut filter so that they can quite easily be adapted to versions that work with bass and preserve low end when needed.
There's also the trick of using a crossover block for simulation of bi amping. Because you have up to 8 paths, you can simulate having a DI signal with different processing too.
Really, it's quite the bass machine if you open your ears and you don't mind tweaking 2 to 3 parameters. My Helix collects dust for modeling and I use mostly as a midi foot controller now because the modeling and control is not at the same level of the Fractal products, even though the Helix may have more things on the surface labeled for bass.