Why my system becomes dull after sometime?

[Audiophile Neuroscience]

There are two time honored methods of fixing flaky electronic devices. a) Reboot by powering on/off. b) Boot, by kicking the device. While B sometimes works I can only really recommend A 😅

[Audiophile Neuroscience]

The conventional wisdom would be power supply issues and I'm not sure this has been as yet eliminated simply by adding a power conditioner (depending on how effective it may or may not be). I would adhere to the advice given about establishing associations or possible links to other electrical components running.

Re overheating, I have an infrared hand gun that reads out the temp of each component, including any part within the pc like sound card etc.

Pschoacoustic variation in pereption is another possibility but that would appear unlikely from your description of unplugging/replugging.

 

If overheating is eliminated and there appears no obvious power issue (like only when air con is running), my money is on your pc