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If you mean the integrated memory tool in Windows it's next to useless for checking stability. You need to run something like Memtest that boots outside the Windows environment. The integrated tool leaves RAM reserved for Windows in operation and that part of the RAM can't be tested. It's fine to diagnose a bad stick but not what you want to run to fine tune things. 8-10 hours of memtest for 8-16GB of RAM.
If you have a Ryzen system there are some excellent configuration tools. If it's Intel you likely won't notice as Intel like the extra bandwidth of faster speeds more than the tighter timings and subtimings that will benefit Ryzen.
A quality external audio interface and optimise the computer for music. (Have a look at the support page for whichever interface you choose, (Stick to the pro market as most HI-Fi interfaces are way overpriced for what they offer) and follow their advice.
Internal components have no effect on music. A good soundcard if you need connectivity and / or an external DAC are your best bet. Some motherboards, especially newer ones have very good audio components integrated. Not flagship soundcard good but close.
If you have a huge collection of music on the PC then put it on an SSD. It won't sound better but it's a whole lot faster to index.
I run my PC's optical output into a DacMagic+. Totally bypasses everything.
Never thought about disabling onboard hardware.
My onboard sounds pretty darn good, even through el cheapo patch cable, a different sound to the DAC, but I wouldn't like to say worse.
I've got a full-on gaming rig, with a Marantz PM6000 and Mission 751s bringing the big noise. I spend more time at the PC than anywhere else, so I gave it a sound setup to match
Perfectly happy with my onboard- although I bought the DAC, so I'm gonna use it! Does vary by motherboard though, shielding, interference susceptibility etc.