What high-end cdp for low-end quality CD's ?

Get EQ.

Marco,
I'd like to correct your statement that confuses some members arround here:

No player even should/must/suppose/ought/oblighed to make or alter the sound of bad recorded/lo-end/poor-sounding/ CD/LP/SACD/XRCD/DVD-A/DLP/MLP/CDD/BCD/BSCD/ABCD/ETC...

Same applies for the well recorded media(s).

You realy shouldn't look in "that department"
It more depends on the further components than on CD-player.

What does it mean "the best darn you can afford"?
Does that mean that if the budget is $20k one should go for Burmester??
There are lots of tricks with digital audio to make it sound different. Heavy clampings, tank-ish constructions, hi-res pics taken from the development lab it's all all to grab your pocket without substantial playback improvement and investing onto it therefore should be very limited.
The price of a raw materials on CD-players that are mostly ICs is getting more cheaper and its quality increases with newer more precise tech-s applied. Hence the price on the digital playback at least should not increase and there should be lots of possibilities getting less costly unit with greater performance. Another way to vary the CD-player performance is playing with feedback levels. At different settings the output will be lower or higher along with the different responce to a load and freequencies. Certainly the deeper feedback will have more linear responce and lower output voltage. This combination of feedback and output voltage on digital playback can be quite differently "interpreted" by further amplification components that as you may know have also different feedback, sencitivity, input impedance, etc etc... characteristics that may or may not by in SYNERGY with your source.
Tube output is a special case that can be applied to any CD-player so the meaning of "tube CD-player" should be considered as misconception or another trick to involve marketing since it's just a pair of dual triodes in inverting differential connection that inverts phase 100% i.e. giving 100% local negative feedback stage. This buffer you can add-on to any CD-player just by simply buying <$100used Musical Fidelity X10 tube buffer that no doubt would act on poor CDs and cheap CD-players quite beneficial.

To my personal knowlege Dennon and Pioneer are the brands that use THE latest models of chips and have highest standards for the digital playback. You will never overpay if you shop arround these components and in case of bad recorded CD you may add-on Musical Fidelity X10 buffer or Equalizer and turn it off whenever you don't need it for the good ones.

Some of the players do have tha tendency:
I've never looked inside the box of such but I would assume that in some of them they should have some dynamic circuitries that would boost bands to it's linear responce once they become less-tolerant(this proccess is realy called a compression that isn't realy suitable for most of the hard-core audiophiles). A regular red-book LedZep II CD with ultra-lo-fi recording quality sounded fantastic through GamuT CD1(BTW fits well onto your budget new or used).
A professional preamps and proccessors have these features switchable and adjustable. Getting a player with tube output implies to applying a maximum 100% feedback to the output signal which can compress signal to the wider bandwidth.
Meanwhile,
I'd recommend checking on the latest Pioneer DVD player with 120GB of hard drive. The initial CD information can be transfered to HD with digital error correction clock that would fill the "gaps" in digital samples(that can occur initially during mastering on any of the CD especially the older ones depending on the release number) thus "curing" the data before the playback of any DVD or CD with pretty darn high resolution proccessing. This unit you can check through Costco wholesale where you can have an unlimited return policy so trial is absolutely free. It features DVD/CD/player/recorder/pro-scan/
Just for my own curiosity despite being pretty darn satisfied with my digital rig I'd go there and try to keep you a company:-)