I figured out that the feedback was, in fact, my fault. I created a loop by running the kb into the 1/4" ins on the VK, and by plugging the HP out (from the VK) into the kb aux in, the volume was able to get outo of control. The puzzling thing was that it only fed back, AFTER I plugged the ipad into the VK. I was able to use it at a nominal volume. This is all a mute point now, sine I've learned that the EK-50 will not fully support my needs, so I'll get a PA700, which has a 5 pin midi jack - problem solved.