Chony and Chris: Yes. you can create a custom drum kit (TVN file) in Tyros3's "Voice Creator". Voice creator allows you to import voices (including wav samples) and map them to specific keys, and then create a drumkit TVN file.
You'll then need to record a snare drum pattern calling up this TVN and save it as a new Rhy1/Rhy2 track in a custom style (such as: Rhy2), then delete the snare drum of the existing midi drum track (Rhy1). Because Yamaha auto accomp supports 2 separate drum tracks, when the style is played, the Rhy2 track should call up the audio sampled snare TVN loaded into your T3, and the Rhy1 track will simply playback the existing midi edited drumkit part.
For more custom drumkit creation instruction details, checkout page 22-23 of Tyros3 Reference Manual.
Scott
PS: Tyros2 supports this as well.
[This message has been edited by Scottyee (edited 10-23-2008).]