I Have the same problem. If I try to add a track an pick out the SI Drums they aren't listed, just cakewalk TTS1 and Mt Power drumkit...none of the virtual instruments.
If I drag the SI Drums into the newly created miditrack, I can open the kit and play them and hear them, but I can't record them and I can't access them on the keyboard by using Alt and 0. It's driving me mad. I can use the MT power kit ..but no effects etc AND..I cant use the TT1 kit....BUT...no fx etc.