For what it's worth, I'm using a relay in my AKSA-100. It's a 120V AC DPST-NO, 25AMP coil rating. Being AC, it plugs directly into my preamp. With a 5VDC relay, you'll need a transformer.
I'm no expert, but I believe a DPST (dual pole, single throw), is safer than a SPST (single pole, single throw).
MOUSER has a good selection of relays.