I have cakewalk PA9, slaved to a 1680, which works great, my pc has two 'ins' and 'outs' but when I try to introduce a midi signal from the VDrums on the other 'in', PA9 freezes up! Do I have to merge the two midi 'ins'? or do I need a midi patchbay or interface? I'm not usually this dumb, but...