Better still, forget using an A/B switch - buy two double pole changeover relays, and use them to do the switching automatically from the Empeg's amp switching output (Orange wire on Empeg harness, unless Hugo's changed anything). You might have to add an anti-spark resistor/capacitor bridge across the contacts, but even then it's going to be pretty simple to construct. If anyone's interested, I'll see if I can sketch a schematic out sometime over the weekend and upload it somewhere.

Dominic

Cambridge Car Audio
http://www.cambscaraudio.co.uk