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.