If I'm reading you correctly, you've done some soldering on things outside both the radio and the amp? But, you, yourself, have never done anything inside either device?
Sounds, in my less-than-professional opinion, that bad power connections are what's causing your problems (from what I read, that's your thought, too).
I'm not aware of any case in which an electronic device has been destroyed by being under-powered (which, if we are correct about the bad power connections, that's the problem ) Although, I have heard of many fires that have started from inadequate power lines; the device was sucking more power (and generating more heat) than the power wires could handle. Big rigs burn from bad power inverter installs, all the time. I'd lay money, that each instance was on account of the power wire not being a large enough guage for the job.
So, then, solidify your power connections. Unless you have shorted something out, you should be good.
I have the same radio/amp combo. I love it. I didn't do any soldering, when hooking it all up. I used some crimp on terminals, so I can remove either device quickly, and I used some heat shrink, to give a cleaner appearance.
I may, later, try my hand at soldering, just to further strengthen the connections on my crimps. But, my crimp method is usually pretty solid.
Incidentally, I have a Stryker 655. It's being stored, and I use the 980/203 setup. Of course, some golden screwdriver had his hands in it, before I owned it, which probably has everything to do with my unhappiness with it. One day, I'll have it put right, and I will try it again.