An old OS is just going to be progressively less compatible with available hardware and software. I wouldn't go that route. Using a current OS isn't going to be any more annoying, all things considered.
You don't need a super high end computer to do audio work until you start doing a ton of...
Pic of my office. Today is "easy," a film festival. I have a theater company loading in tomorrow. Some productions have separate sound and lights ops and a stage manager calling cues. Some will integrate lighting cues into QLab and the stage manager will just hit the button.
Here's a typical 2x2 interface. It entirely replaces the function of your headphone port and much more. There are cheaper ones, this is just a common one.
https://www.sweetwater.com/store/detail/Scar2i2G4--focusrite-scarlett-2i2-4th-gen-usb-audio-interface
The transformer is built into the...
There are a couple of these where I work. They seem to work okay. There's a stereo version.
[Edit] I have no idea if this will cure your noise problem, but it does have a ground lift and presumably uses a transformer...
A generally more reliable solution would be an audio interface (AI, ironically). Another possible solution would be a passive stereo direct box with a ground lift. I'd just go for the AI. Ideally, connect via balanced cables and connectors.
I saw Superstar on what was probably it's first run in Los Angeles. It makes me wonder how they managed to get a similar effect with a presumably entirely different lighting system.
I ran the recording through Spectralayers. The software wasn't able to consistently distinguish between the guitar and mandolin. Sometimes it would appear on a separate track, sometimes it would stay mixed with the guitar.
In this case, he's trying to sync up things recorded on tape and digitized separately. It's not so much about being perfect but about making the error of one match the error of the other. Also, there are different kinds of imperfection. Tape speed is a different thing from frequency response or...
You suggested that doing digital processing that affects pitch was a bad thing, but you seem to be okay with analog effects that do exactly the same thing (except that the analog effect makes it less like the original performance while the digital process makes it more like the original...
When you play analog audio and the speed changes, it's causing pitch changes. Using stretch or squeeze to compensate exactly reverses what happened in the analog playback, including correcting the pitch changes. If you cut and shift clips of audio, you're failing to correct the pitch alterations...