I think for differences, PB has
stereo mixer
dust
snare
sequencer
deerhorn
there is verso/inverso control for mixer, rolls, avdogs, gongs, snare/dust
avdog is stereo, has fm in with attenuverter, cv out, and l/r audio out jacks
gong have fm in with attenuverter, cv out, offbeat out
ultrasound filter has cv in with attenuverter, and cv out
avdog and gong have 3 way toggle for off, trad, or gonzo mode
avdog, gong, and deerhorn have stereo aux inputs
2x 4 roll with rate knobs
2x 3 roll with rate knobs