Hello
Again sorry for the bad english …
A very good drums app (best on ipad I think) and free! :
DMtouch
Designed to work with an ipad/pad drum kit alesis it works very well with Cubasis (IAA in audio track controlled by a MIDI track). No need audiobus.
Everything is adjustable, each tom, each instrument. One can compose and saved his own kit, mix table with fx , pan , volume.
electro sounds, acoustic, beat box, percussion. Enjoy !
You will tell me what you fink of this 
Good music all