ESOTERIC, WADIA -- How do they really sound?

it's all a matter of personal prefference.
that's why you see different things being said.
at times same component performs differently in the context of different systems. what makes you concentrate on the Esoteric and Wadia? what do you currently have that you need to upgrade?

Saxo, what is almost universally true is that even those digital players that have a volume control do in fact benefit from a linestage. You may think of the volume attenuator in the player as something to be used 'in a pinch'. Most of my experience is on the TEAC X-01 in its various incarnations, which by the way does not have a built-in volume control and needs to be used with a linestage at all times. I am not quite sure how the device can remotely be characterized as mechanical, thin, reedy, flat, lacking dynamics, or of possessing any of the various stereotypical defects routinely lobbed at digital players. The device has tremendous dynamics and very subtle microdynamics, a soundstage to die for, tremendous extension, exceedingly detailed and -- at least for me and so many other audiophiles out there -- it embodies the word 'musicality'.
All of this. . . provided the unit has been properly broken in, with at least 800 hours of playing time, otherwise all of those negative stereotypes will apply without reservations and in spades to boot.
Having said that, I also said so many times that there is no absolute best. You may love the intense beauty of the sound generated by products of this brand, or you may not. You may very well prefer a slightly more 'romantic' presentation afforded by some other make. In the Esoteric line I suggest you have a listen to some very well broken in units of the X-03 SE, the X-01 Limited, and if you preferred a slightly warmer sound and your budget allows it -- the P-03/D-03 combo.

These extremely rarefied products are usually critcized by
those who don't even own them and invariably have an agenda you will identify if you are able to talk to them.
The comments you mention certainly don't apply to these fabulous products from exceptionally reputable companies.

if you feel unethical about taking pieces home from a dealer when you plan to buy used, why not bring in a favorite CD to the dealer and listen to it there?
assuming it isn't too busy and you're not depriving the salesperson of a possible sale to someone who'e really there to buy, it's no big deal.

by the way, your first sentence (about upgrading the source making the greatest difference) should be taken with a grain of salt: getting a source which is way better than the rest of your system isn't necessarily a good strategy. it makes more sense to look at your whole system, including the room, interconnects, etc. before deciding on upgrades. people on this site can be very helpful if you tell them what components you're working with, your musical tastes, preferred volume level, etc.

Saxo, One of the great trade-offs with buying used, is that it can give you a free education. Once gear at this level takes it's first big hit (to about dealer cost) it seems to level off for a while. Buy and Try I call it. You may find that these toys are the first to go when money is tight, so if you are truly able to play at this level, you can occasionally find pieces offered below market. Then off you go to your dealer, probably armed with more product knowledge than any employee, and negotiate your best deal. To answer your first question, they sound really good! Happy listening!