Ez ear, to date, I have not been too creative with the tubes in my Doge 6 CD players. You might be aware that Pacific Valve has a decent stock of tubes - both new reissue tubes and NOS tubes. The staff at Pacific Valve has experimented with various tubes in the Doge 6 CDP, so I trusted them to recommend the upgraded tube complement. You can check my virtual system threads for the specifics, but my recollection is that they replaced the four 12AX7s with Tong-Sols and the pair of 12AT7s with 1987 JAN Phillips tubes. The cost of the six upgrade tubes was modest (less than $100), and the sound is excellent. So I have not, personally, gone any further to experiment with alternative tubes.
As an aside, I would advise caution in putting any faith in the high-endaudio.com shootout findings. To put it mildly, there is a lot of controversy swirling around about that shootout. You can read all the dirty laundry over at the Asylum if you are interested.
Nonetheless, the Doge 6 is really an unbelievable value. When you see the build quality of this unit and hear the level of performance, you will be impressed.
By the way, as good as the Doge 6 is, it really is not in the same league as the AMR CD-77, which IMO is one of the very best SOTA digital sources currently available, regardless of price.