I don't know what experience others have had with MIDI interfaces but I've tried several and the only one to give good results has been the Roland UM-one MK II. I'm using Windows 8.1 64 bit.

Strangely, after installing the Roland UM-one MK II software my KN7000 started responding to MIDI over USB perfectly and I'm not sure whether this is peculiar to my setup. So, I don't actually use the Roland UM-one MK II for most operations now (but it does give slightly better performance than the USB when I do. The difference is marginal).

I definitely wish I hadn't wasted a lot of time and consternation with other interfaces so posting this in case it helps you,