I have a 1.1 and its great for Bass - there are even Bass presets in the factory memory, up near preset 30 onwards,
Sounds way better than the PT plugin too.
Adam Deuce Bass player of Machine Head uses one blended with an Ampeg SVT,
My Ampeg SVT5 Pro has a overdive channel that you can blend with the clean output to get the same effect (clean punch & distortion growl),
Havnt tried the PSA1.1 with my ampeg but it did work well with my old Trace Eliott Head for that kinda sound.
I like its sound for guitar too but the presets are not really that "modern sounding" compared to the kinda sounds people are shaping on this forum but still good,
More like 80's 90's Marshall JMP1 type sounds as far as i can tell,
I like it for guitar and bass but needs to run through an amp/cab or cab impulse for guitar to sound best.