Avast there mateys!
Actually you can crossfade sounds using the TD-20, however, it sounds rather wired because the Roland midi note numbers are not in any sequence, so at one velocity you get a snare hit and withanother velocity yu get a cymbal and with a third you may get a sound effect. It's great if that is what you want, but most of us are trying to acheive something a little more civilized (this from a Pyrate). I did not find the crossfade particularly useful in my TD-20 setup because of these limitations. It would probably be fantastic if using something like BFD.
Fair Winds and Following Seas,