Sound systems are complicated to figure out, dont be afraid to ask a billion questions. I've always had to lol
Anyway, what I would do if I were you, is use that 4 channel amp for something else or sell it. You can run two subs of a mono amp as well, if you wire things correctly. And this would be the proper way to do it. Subs won't ever like 2 channel bridged amps quite as much as they like a mono amp, because a mono amp is made for subs, essentially (Lower frequency responses, different circuitry, etc).
I have a dual 2-ohm voice coil Rockford Fosgate P3 10" in my truck wired to 4 ohm, because I have an 1000w amp that puts out 600wRMS at 4-ohms and my sub is rated for 500wRMS.
The cool thing is about this setup, is that if I decide later on that I wanna add a second of this same sub, I can wire it to 2-ohm and then have 500wRMS going to each sub because my amp puts out 1000WRMS at 2-ohm.
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Thats how mines wired right now.
but if I wanted to change it to two subs and still provide enough power to each of them, I could change it up and wire it like this:
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A big thing about sound systems is wiring and wiring it properly. Its more than just being about power and ground, impedance is huge in this application.
And make things as tidy as you can. Loose wires is never good... as well as a safety hazard.
