good/best CD player with variable out

I third the Audio Aero recommendation, the most musical player I have ever heard.

I have to confess that I have never personally tried the Audio Aero Capitol, I have only auditioned it at the shows. I did try the Wadia 861 and my own Accuphase 75V connected directly to my amplifier, and they did not sound even close to what you get through a good preamplifier !
I think that all our recommendations might help, but at the end if you have the possibility to perform a test, that is what you should do.

Audio Aero Capitole MKII is highly recommended !

AA has high quality analog volume control and high output impedance that would be perfect match with your tube amp or any medium input impedance SS amp.

You like having a good tube preamp,DAC,CD transport,2 interconnects,and 2 power cords which would cost you more than $20,000 to get the same performance.(I'm not kidding)

Simple the best !

Depends what your budget is.
If you have a big budget, I would not suggest running a digital source with variable volume into an amp.
A great active preamp make a system sing.
If you are on a budget, well going digital direct into an amp, is an option.

KF

Put me in for Audio Aero too ! Brilliant tube magic sound. You must wait for it to break in. I it better than the wadia 850 (too in your face with detail), or the levinson (boring) near as much as the AA.

In general I agree with Tok20000. The AA is the notable exception. It's tube output stage is so dynamic, smooth and musical you WANT to hear as much of it as possible. If you don't care about tuners or analog, the AA is head and shoulders THE best cd playback I've heard. If you want to go really cheap, the older sony xa7es's are pretty good for $900ish.

Aa alternative is to pick up a used (or new) placette passive preamp. Mate that with a cheap transport and a Bel Canto DAC 2.0 (or whatever floats your boat). Provided a source component has a reasonably robust output stage, the placette's compete with price no object preamps. If your source component has a wimpy output stage you will experience a lack of dynamic drive. Personally, I hate it when that happens. With my main system's mondo-output stage source components (hotrod scd-1, MR-78 tuner, Cal Alpha DAC, Pass ONO), I find the placette gives greater resolution than a high quality preamp.