Pacific Valve offers modified Lite DACSs with a return option (less a reasonable restocking fee). Other tube-based DACs are also available from retailers that will take them back if they are not what you had hoped for. One example, the Music Hall DAC can be found at Music Direct with a 30-day return option.
The reason I suggest this approach is my own experience. I tried a tube-based CDP as a potential upgrade to my Rotel RCD-02 (a step down from your player). I could hear no difference whatsoever in my system with the new CDP. I concluded that the rest of my system was not resolving enough to portray a difference that most audiophiles say should be obvious and dramatic. Since then, I've upgraded my preamp, amp, cabling and am about to upgrade my speakers. Once I am done with that (and my bank account recovers), I will be looking at upgrading the Rotel player. Good luck!
