Add an external DAC. Make my Oppo UDP-205 a true top player

OP, you’re going to get LOTS of DAC recommendations, most of them for highly rated units. Like everything else in our hobby, once you get to a certain level all the choices are good. It comes down to system synergy and your ears to determine the best fit. Try and buy from a vendor that has a decent return policy so that you don’t get stuck with something that isn’t a good fit. I happen to be fond of my W4S DAC, plus their DAC’s are upgradable.

What specifically are you looking to improve upon, are what overall sound and performance characteristics are most important to you?

Jrwaudio, got the PLUS power supply,  upgrade power cords and USB, umbilical? If not, you have some potential improvements on horizon.  :)

Truthfully that oppo measures incredibly well.  If you don't like it's sound signature, I would go in the opposite direction to get a different flavor.  

Look at an R2R, or something that doesn't use Sabre Chips.  Heck, maybe a tubed unit.

But the Oppo uses killer chips, and has a nice power supply.  

Prior to selling my 205, I found a large improvement in sonics by placing a Vibrapod 4 under each foot. I never found Vibrapods to do anything particularly worthwhile in the past, but they seemed to make a significant improvement on the Oppo. You might even have some lying around. Cant’ hurt to try. Well, I guess you would be out $25 or so, but that’s not much in the audio game.