Bloody 'ell, what a mess!
Yesterday afternoon I decided to tackle my PC's sound production problem, which you might recall is, or was, that the left rear speaker either produced distorted sound or no sound at all. I did the normal jiggling of connection wires/cables to no avail other than occasionalyl switches from distortion to nothing and vice versa. Decided to remove my Yamaha 4-channel power amp and substitute the amp section of an old NEC a/v receiver collecting dust on a living room shelf.
Man o man is it heavy! Which is why I've been reluctant to make the switch. Made the move easier for myself by placing a desk chair with casters next to the NEC, transferring the receiver from shelf to chair, rolling chair to the computer room, then transferring the NEC from chair to its tentative new home. Even with the chair the small amount of lifting and carrying I had to do was very nearly too much for me.
NEC in place, I removed pre-power amp bridge devices from the four channels I need to use. Installed banana plugs on all four speakers cables at the receiver end. (Neither the Yamaha amp nor the speakers themselves accept banana plugs.) Hooked up speakers. Hooked up RCA audio cables Booted computer. Switched on NEC.
Eeeeep! While clean sound emitted from all four speakers, it was accompanied by loud hum, noises and crackling. Spent the rest of the afternoon and much of the evening hoping to solve that, to no avail. In the process I replaced all speaker cables (which needed doing in any case) and rerouted cabling to avoid electrical interference is so far as that is possible (which also needed doing). Reconnected the NEC's pre and power amp sections, and attached the PCs audio cables to the NEC's External 7.1 device inputs. Nothing helped.
There came a point when I knew I was better off with the Yamaha and its one flaky channel. A regrettable lesser of evils as it were. Removed connections from the NEC, removed the NEC itself (poor back), removed banana plugs from speaker cables, put the Yamaha back in place, restored its connections to the PC, booted the PC, switched on the Yamaha.
Now both rear and FRONT left speakers produced distorted sound! Nothing I tried fixed it. I had one last trick up my sleeve, one I did NOT want to resort to since it forces me to run in 2-channel mode. By then it was well past 2300, too late to try my last remaining option and get any sleep at all. Went to bed. Managed maybe 2 1/2 hrs shuteye.
Starting back in before breakfast, Removed connections from the Yamaha, removed the Yamaha, restored banana plugs to speaker cables (sigh), yet again set the NEC in place, hooked up speakers. Here comes the difference. Rather than use RCA cabling to connect PC to NEC I opted for S/PDIF, with its regrettable 2-channel limit. Fired up the PC. Configured PC for S/PDIF. Switched on the Yamaha. Set Yamaha to use its S/PDIF input. Tested. Clean sound. No dead channels, hum, noise or distortions. Success, with the big caveat of losing discrete 4-channel mode.
I can still utilize my two rear speakers thanks to the NECs many surround-sound options. Applying one of those makes music and speech every bit as good as, and often better than, the PCs discrete 4-channel mode. The bummer, and its a major bummer, is that I've lost all sense of directionality for sounds emanating to the rear in Oblivion, and I assume Minecraft and other games. That's gonna be hard to swallow. Very hard.
As if all this isn't enough....all of a sudden my PC monitor will not wake from sleep mode! The computer itself wakes just fine. Not that it matters. All I can do is switch the PC power supply off and on, wait a few seconds and turn on the computer. The monitor responds normally to a cold boot, until the first time it enters sleep mode, when the cycle begins anew. Disabling monitor sleep in Win10 power options does not prevent the monitor from sleeping and not waking. What a mess. Which is where we came in.
Holy Cow! You are amazing! I had some problems like this years ago, and switched down to one mono speaker = that was my solution! You are really Awesome!!! (and tenacious!)