How easy would you think it would be to have the arranger playing on the xp and have a sound from the Korg playing in the right hand?
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If I understand you properly you want to use the Tr's keyboard to play the Genesis (styles or sounds) with your left hand and the Tr's own sound with your right hand. That's possible but very hard to do. You have to program (split)every single Combi you want to use (up to 381)with one track set to the left side of the keyboard in external mode to control your Xp and the other 7 tracks to the right side in internal mode(you will lose one sound in the case the original Combi uses the 8 tracks). The Tr has no button for split mode(like arrangers) which would be very useful for this purpose. Another option is changing the Tr's sounds "inside" the Combi manually with the data wheel(only one track at a time) but the effects won't be changed. I would love to use the Tr's keyboard with aftertouch as a contoller but actually I use it as a module. Indeed if you still want the Tr's sounds you can buy the Korg MicroX as a module(with similar sounds but more techno oriented) at half the price and a 76 key controller. Good luck.