The "dropout" difference between keyboards is not only in the voice allocation (voice stealing algorithms) but depends if the keyboard uses layered sounds. For example the Roland JV can use up to 4 tones per soundpreset which means if you have 64 voice polyphony and use such a 4 tone presed you get an effective polyphony of max 16 voices.
Probably the Pa-X works mostly with single tone presets.
Question to a Pa-X owner: try to play a MIDI file (a bit busy one) and then play the piano live over it, making use of the sustain pedal.
Are or are there not voice cuts, dropouts etc ?
Many MIDI files need quite high polyphony and piano with sustain pedal too so I think regardless of the good voice stealing algorithms there will be voice cuts at some point.
If there aren't then the polyphony must be higher or other things we are missing. As said I don't own the silver beast, nor did I test it somewhere so I cannot make any judgment.
cheers,
Benno
http://www.linuxsampler.org