i admit i've never compared the pricy stuff such as accuphase & wadia - i guess i can't afford to wring that last *nth* of sound from a format that i never really liked that much, & is in imminent danger of being replaced. but, as far as more *reasonably* priced cd players go, it has been my experience that a preamp is a positive addition - even to the resolution audio cd50/cd55, which has been lauded as a great cd-player run straight-in to an amp. i was willing to spend up to, say, $1500, for a used resolution-audio cd-player, but i honestly found no meaningful improvements between this player & my $500 nad cd-changer, when run thru my melos preamp.
so, if ewe can afford a mega-buck cd-player, mebbe it *can* sound better run straight-in than when run thru a preamp, i dunno... but i do know, at least for me, anyway, that a less-expensive cd-player can definitely be improved by a top-notch preamp, and the preamp will, in fact, level the playing field between most any reasonably-decent modern player from at least $3k down to a lowly $500 cd *changer*. and, if ya listen to other sources, w/a great preamp ya get the benefits of great sound w/them, too! ;~)
one persons' opinion, doug s.