Is there a bass synth in the HX Stomp?
There is, yep, though it's probably the weakest point in the Helix range at the moment, and Line 6/reviewers are pretty honest about it. L6 have hired a bunch of polyphonic experts apparently to work for them, so the future will be interesting.
I think that's the other part of the Helix/modelling world that I like. For the most part, there's no huge push to upgrade. The incremental software updates and improvements make it worth it instead.