heh, easiest way out, try the de-7 with 2 out going to 2 different amps
if you doesnt hear any abnormality of hum or signal weakening situation(phase cancellation). Forget bout the ground loop and phase cancellation issues and play the instrument.
but if wanna more info, just google on eliminating ground loop/cause of ground loop, signal in phase/outta phase/phase cancellation. There will be plenty of readings and more accurate then what we can explain here.