My band highly integrates the use of synthesizers all running through my software on my computer. So at live shows, our drummer and our vocalist both have MIDI controllers that link up to my laptop, which has all the software synths, samplers, etc., mixes them, and then sends the signal through the headphone-out to a direct-box which goes to the PA. This here has no problems. But i was thinking of maybe doing some bass synths thru my amp, using my laptop synth setup. I have a GK 400RB-III, and I was experimenting running the computer signal straight into the input and the effects return of the amp, and both instances resulted in massive humming, processor noise, and some other crazy things. I thought, the signal in the effects loop is line level, and the signal coming out of my laptop is prolly line level too; but apparently I'm wrong. Or maybe I have some impedances mixed up? anyways I was wondering if theres any way I could get my "headphone-level" signal to turn into a line-level or instrument-level signal.