I agree with amping them...yes, they are designed to be low impedance portables that can be run from portable gear without the need for an amp, but these sound fantastic with one. Much improved bass response, clean highs (they already are, but amping the phones gives you a lot more "overhead"), and a slightly more forward midrange. In fact, I am stunned by how much low end bass these phones are capable of...the Arrow's bass boost makes these phones just pound, while maintaining control and clarity. The low end is there even unamped, but it tends to be hidden by the sparkling highs the T50p's are capable of.
I don't find them veiled at all...very clean and clear throughout the frequency range, especially in comparison to the ESW9's, for example. If anything, the vocals (not the entire midrange) seems slightly recessed, but I think this is due to the bright highs and smooth bass.
OP, what version of the earpads do you have? I can't remember the exact serial number, but I think somewhere around the 3,000s they switched to a broader, flatter and more open earpad in order to address the picky placement issue...the older pads made it difficult to get a good acoustic seal on the ear, resulting in loss of bass and overall sound signature.