There are isolation boxes that I expect would work. My desktop at home is in a big case with a lot of ventilation and a couple of large fans. The fans are so big that they barely have to move to keep the case cool, so they're pretty quiet. It's so overbuilt that it barely breaks a sweat, even on...
Condenser microphones generally need to be powered by the device they're connected to, typically a mixer. It's called phantom power, and a 1/4" mic input won't supply it.
Many digital mixers are capable of recording multitrack onboard and/or to a DAW.
I have a UI24R, and it's pretty effective for live mixing and recording. I haven't tried it in a studio setting, but I think it would do reasonably well. It records to a USB stick, which has to be fast enough and...
You should probably engage the pad on the mic itself. The active circuitry in the mic can be overloaded by loud sources. Decreasing gain downstream won't undo that clipping.
I use two mics on a snare and I never worry about polarity because the sound of the bottom has almost no resonant elements. It's pretty much just the white-ish noise of the wires. And I high-pass it so what little it has in common with the top is further reduced.
On a guitar cab, I definitely...
I record the whole band live, maybe without the vocal if they know the song well enough, and replace as needed. My goal is to get a complete drum take to build on. I'll generally have the bass, guitars etc. go direct at this stage, then mic them for real takes.
But this all requires having...
Bit depth (word length) mostly sets the digital noise floor. I would bet the guitar has enough noise that 16 bit audio won't be the weak link, as long as your gain structure is decent (don't go into the reverb with very low levels).
What unit?
If it's a tape machine, you're going to be spending enough on tapes to make a computer look pretty attractive in not very long. Getting it serviced will seal the deal.
You don't need a super special computer or an expensive DAW to make great recordings. I record on an old Win7...
The connection may not behave well with the Mackie's input rings grounded. It should, but that doesn't mean that it does. What happens if you partially insert the plugs so the tips connect to the socket's rings?
If the connection is balanced, lifting the audio ground(s) might solve it. Lifting power ground as a diagnostic test is okay, but it's technically not the correct solution.
No, it was a known issue with at least some of them, and it was something that I heard about by the mid-80s when the mixers were probably less than a decade old. Other mixers that suffered the same treatment didn't have that problem.