PowerWave should work fine with any 225/45 card that will fit in the slot.
The PowerWave is essentially a (take your pick):
1) 7500/8500 with the video circuitry removed.
2) 9500 with the second PCI bus removed.
It might not (or might) work with a 210/60 or 240/60 card. I've had the PowerTower Pro and Umax S900 up to 62MHz bus speed, provided the CPU card properly sets the CLKID pins on the CPU card.
I think I covered the 8500/8600 stuff in another thread when you were getting the PW working, but in brief:
Three revisions:
PowerMac 8500/9500, 8600/9600. 8600 Enhanced/9600 Enhanced.
The "enhanced" models are the ones with the "Kansas" motherboard and the "Mach V" CPU card which uses the PPC604ev chip.
Apple's CPU cards 250MHz or faster were PPC604EV, Mach V, cards which only work in the two late, enhanced models.
Some third party brands sold 250 MHz PPC604e cards which will work in all the non-enhanced models, both Apple and clone.
All of the non-Mach V Apple cards, PCC cards and Umax CPU cards should work in the PowerWave and PowerTower Pro.
Except for the PowerTower Pro and PowerWave, Apple CPU cards will not work in the Power Computing clones.
Also, PCC cards made for the PTP and the PW may not work in the other PCC clones. The other PCC clones are based off of the Catalyst chip set and need a couple of CPU signals which aren't brought out to card pins in the Apple cards (and the PTP/PW cards?).
But, that doesn't matter, because you're testing a PowerWave. That 225/45 card should work, if it is functional.
If it is a Umax card, then there are three (four?) jumpers that need to be installed at the top, because Umax had this weird double-processor scheme with a ribbon cable between the CPU cards and when the CPUs were used singly, some of the cable pins needed to be shorted with jumpers.
Hopefully you're testing with no cache installed. Those can cause issues. On the other hand, I've read of cases where things didn't work well until a cache was installed. I guess the extra load reduced ringing on the bus or something.
Finally, what it really sounds like is that your power supply is marginal and when the load gets above a certain point everything goes flakey.
Do you have another ATX power supply on hand you could try?
I've also seen the PCI bus on a PowerTower Pro fail because the solder joints on the PCI arbiter chip went bad. PCI arbiter is a little square PLCC chip, with 20 or 25 pins. I don't remember the markings at the moment.
Oh, and, having an older 132 card work and a newer 225 card not work, I have seen when there were problems with the 3.3V supply on the logic board.... Just remembered that one from about 15 years ago.
You might take a voltmeter to the 3.3V supply, although if it's something like worn out bypass caps a voltmeter might not tell the story. In my case, one of the chips had developed an internal short that was loading 3.3V to one of the other rails, or ground, can't remember which. It wasn't enough to shut down the PS, but it made anything that wanted 3.3V not work. But it could just be that the old PCC power supply isn't supplying good 3.3V, in which case a repalcement ATX PS will solve that.