I have a level 2 PDX with Bybees all over the place as a special order. Like I say its the best DAC I have heard so far with one exception (aside from the Killer which may be better) - a Playback designs DAC I have on DSD - but only DSD - via PCM the PDX easily bests it - and of course its not valve.
Each DAC is hand built by the designer, Clay Geisner, to order, and the output resistor is adjusted to the input sensitivity of the amps being used. This is to make for easy direct connecting to the amps and using the volume control on the computer which myself and others found sounds the best. Its a bit better than the version with the volume control even though the particular volume control used is very transparent using LED's and not a pot.
No op amps or anything like that. The power supply is a special linear supply that plugs into your outlet and connects by a special supplied chord.
If you want to know more simply drop Lenehan Audio a line. The guy that runs it, Mike Lenehan, is really good to deal with. I am fortunate to live only about 30-40 minutes (so does my mate Doggiehowser) from the factory and know the guys there pretty well.
With the amount you have to spend I would look at the version I have with Bybees all over the place (on the power going in, from the DAC chip to the amp, and on the output). Its not on the site but just mention it to Mike and I am sure he will arrange for it.
Anyway good luck on your search.
Thanks
Bill