dac advice

I like the Centrance DACmini. It goes for $795 (new) and has a nice headphone amp as well. I haven't hear the others you mentioned.
The one word I would use to describe it is--clarity. It sounded great and when I got a media app (BitPerfect) it really came to life. Remember, its the way it works in your system that makes or breaks the deal. Having a tube amp would be a big plus as the DACmini is quite adept at pulling out all the details.

Good luck in your search

Again, if you want to stay within you budget, check out the DACmini.
Centrance licenses out their tech to the likes of Benchmark, Apogee, Lavry and lots more who wish to remain nameless. They are a 3rd party design firm for most of the chips out there. They also consult to Apple and some PC makes. Top recording engineers use their products as well as other artists. Their latest DAC chipset is one of the best designs out there right now. Don't let the size fool you: it's all in the implementation.
Checkout the reviews at 6moons, Enjoy the Music and PFO. You get a lot for the money.

One more thing---you can a DACmini from somewhere like Audio Advisor and they have a generous 30 day return policy. Just keep it in great shape. I got mine direct from the source and feel no need to give it up.