From your previous query on the pre-amp, I'd third the recommendation for the Cary SLP-50(A). A real sleeper of a design and can be had very inexpensively on the used market. Sounds wonderful in my system and easy to resell if you don't prefer it. Don't be afraid of tubes, they don't bite and you can replace them when they die.
For $500+ you'd probably do better buying and all-in-one player. Yes, the transport does make a difference. Sony makes some good players, including some capable SACD players that can be had in that price range used like their 555. Also used you could look for a Rega Planet 2000, and Ah Tjoeb 4000, or a Jolida 100, the latter two having tube-output stages. If you insist on the DAC/Transport and must stay in your budget, the only thing I could think to recommend, for just a bit more, is the CAL Sigma II DAC and a decent transport like their Delta. Again, this is a tubed DAC. Had one a few years back and it sounded great! The transport they made, the Delta, is good too, but be forewarned the company is no longer in business. Still damn fine gear for the money.