Your problem with sound quality is most like with the sound card on the none HP PC if it the sound quality is acceptable when played on the HP PC. I've tried some quick tests and have found the sound card to be a potential area for poorer sound quality. These days a good sound card can cost twice as much as some PCs. Compare the specs between both sound cards to see if there is a difference.
Cheers
Logic is a systematic method of coming to the wrong conclusion with confidence.