Many thanks for all the info!
Although I figured something was wrong because DOpus wouldn't run, I went for broke and installed OS 3.9, and lo and behold, DOpus runs after 3.9 was installed! It's beyond me...
I'm using the stoak A1200 power supply, and that could indeed be the problem. I'm also gonna take a look see with SnoopDOS.
But for right now I'm gonna take a break and clean up all the blood from where I've been beating my head against the wall the past few days :-D
Thanks again!