Looking at the Decware amps and wondering if my current REL powered subwoofers setup using the "high level" connections directly to the speaker terminals will work on the Decware amps. The REL connection in this instance requires that there be room for two spades to be piggy-backed and clamped together by the positive terminal in addition to the banana connector speaker cable, ie the REL connector spades have to have enough clamping room underneath the terminal. The REL ground spade has to also have clamping room underneath the ground speaker terminal. I can't tell from the site photos how far the Decware terminals can be unscrewed in order to accommodate these extra spades.

Since you have 2 subwoofers, hook them up as normal, they will work fine with Decware amps.

Geno's advise is correct if using a single sub.

Pretty much. I don't think I'd go smaller than 20 awg.