Trouble with headphones

Here's a little story: A few years ago I owned a Dell Dimension 4600, with Windows XP 32-bit, which came along with a pair of Panasonic RP-HT360 headphones. These headphones had astounding audio quality and very comfortable earmuffs, that plus they lasted a very long time. A while passed before the RP-HT360 broke and I had to get some new headphones, I chose a pair of Sentry HMM10 to replace the RP-HT360s. The sentry headphones were cheap, small, but had a noticeable decrease in sound quality when compared to the Panasonic headphones. As a note, I bought the Sentry headphones while I still had the Dimension 4600 / Windows XP 32-bit.

Now, a year later I purchased an entirely new computer, an HP e9120y desktop with Windows Vista 64-bit. Along with purchasing the computer I also decided to buy a new set of headphones, I bought 3 different pairs, all from different companies, but I had to return them all because their sound qualities were actually worse than the $5 pair of Sentry headphones. Obviously I was very surprised at this, seeing as a pair of not 1 but 3 different headphones which cost an upward of $50 each had worse sound quality than a cheap $5 set. Then I finally decided to re-buy a new set of RP-HT360 headphones, the only headphones that I absolutely knew for sure had better sound quality than the sentry ones.

But here's the problem, when I purchased the new set of RP-HT360 headphones, they also had worse sound quality than the Sentry headphones. I was dumbfounded. The last time I owned these exact models of headphones, I knew for sure they had better sound quality than the sentry headphones, not the other way around!

I'm starting to suspect that this mystery has something to do with my computer, or operating system, seeing as the Panasonic headphones only had better sound quality than the Sentry when they were used on a 32-bit Windows XP operating system.

Help?

 

The sound quality is worse in the sense that it has overall lower frequencies and less clear sounds, try to imagine listening to a radio while your head is underwater, that's what the Panasonic headphones sound like.
And the overall sound quality is affected through all uses, Music, videogames, movies are all affected by the lower sound quality.
And the computer is actually a factory-refurbished, older computer built in 2008, relatively old but with decent specs.

 

Actually, the Sentry headphones use the lime plug, the Panasonic headphones are USB-based.
I'm not quite sure about the sound controller, I'll look into that.

EDIT: Yes, I've found a Realtek Audio Manager on my computer, I'll trying tinkering around with the settings to see if it fixes the problem.

 

Definitely not, the headphones are just headphones, and believe it or not they use the USB jack instead of the standard Lime one.