Nick I had the BK7-M and a GW8 and the bass sounds are about the same. Average to bad. Same with the guitars, especially electrics.
The BK's are supposedly loosely based on the Fantom (although much smaller and compressed ROM samples)) and the GW7 based on the Sonic Cell, again with a smaller size sample ROM. And no expansion card option.
Doesn't really matter as I remember a LOT of the same sounds on the SC88-Pro
...actually some as I recall, sounded better on the SC88.
FWIW if the sound engine doesn't cut it for me then I usually do not bother with the rest...
With the PA3 I have now accepted compromise. Not as good as the Yamaha Motif XF when it comes to B+B (not even the Kronos can match the Motif's on that score)...but way better than anything on a Roland, and apart from S.A. the Yamaha too.
The module was a real p.i.t.a. for any sort of real time mixing control, ore any control for that matter dunno about the keyboard version....
As for the other questions, no exp with doing that so no comment...
jm2c
Dennis