Hmm ... HPs tend to be a bit problematic for what I was going to suggest ... they aren't really PCs in my opinion, they're HPs.
Where I was going is to suggest getting a soundcard. A cheap soundcard is 100 times better than onboard sound (which really only give you the speaker/headphone connections ... all of the sound processing is done by the CPU, in contrast to a soundcard that does all of it's own work).
An old HP may or may not have an available slot, and if it does chances are it will be an ISA slot rather than a PCI slot (and ISA soundcards will be hard to source).
Having a look inside the case (and if need be comparing what you see to pics off the internet) will give you a better idea. At the very least you'll have an opportunity to blow out some dust bunnies while the box is open.
- Edit - PCI slot vs ISA slot
Edited by Striker879, 02 May 2020 - 11:21 PM.