Budget cd player or newer HD cd/dvd player??

Right now I'm running a Sony dvp ns75h as my source. It's a high def cd/dvd player. What I need to know is if it's worth while to purchase a dedicated cd unit. Will it sound better?? I was looking for something in the $0-$350.00 range used. As for the rest of the system, it is old NAD stuff (1020b pre, 2 2155's in mono).
It does sound good as it is, but wonder if a decent cd player will sound better? Or should I keep the source and use the cash for a good DAC unit?

Your help is appreciated, Thanks.
I am very pleased with my used Denon 3910. It was in your price range, sounds great, and plays almost everything.

the sony looks like a well-regarded budget piece--if you still plan on watching movies, i'd keep it and add a dac, such as cambridge dacmagic or mf v-dac--both within your budget. if you're only using the player for music, i'd probably replace it with a dedicated cdp--used cambridge 640 or nad are probably the best in your price range.
Another vote for the Denon DVD 3910...really hard to beat for $300ish on the used market!!!

...and should you someday decide that a DAC is in your future, it's a solid transport.

Good luck!