i have auditioned a number of them and something is wrong. i perceive a dip in the 100 to 200hz region and a slight peak in the upper mids/lower treble region.
What is your reference? Have you made calibrated microphone tests of what is wrong?
is it possible that one can buy a current production player which is 20 bit and no up sampling ?
Sampling is a time based thing...higher sample rates or up/over sampling can make output filters simpler to design.
I suspect that the designers are simply using a 24 bit/96 Khz DAC and are upsampling the CD data...you can't get 24 bit dynamic range from redbook 16 bits (physically impossible unless some kind of "expander" algorithm is used and this introduces distortion) and therefore I imagine the extra 8 bits are not used. (So don't worry about the extra bits as they are irrelevant in the case of redbook CD)