+1 on Garfield's comments here. People shouldn't be trying to feed synth-level signals to outboard devices. OF COURSE it'll sound like it's leaking...because you're taking about signals that can swing up to +/- 10V, and feeding these into something that either wants to see 1.4 or .775V. Since you're an audio tech, I shouldn't have to explain why this doesn't work, and also why an isolated, balanced output will improve matters as well.