I have found that my X5 sounds a little improved using the line-out and an external amp.
With my se530 - using a slee voyager portable amp. the iems sound a little more full/deep especially with bass guitars/double-bass and more liquid in the mid-range, alos (and the reason I use them - the treble has far more sparkle/weight). It is only when I listen careful is the difference is noticeable to any extent (apart from the treble) though and for casual listening or using them in more noisy environments, the difference would be negligible.
The same happens with my nad hp50 and I use a neco soundlabs (uk) amp. with these as the synergy is better than with the voyager.
So my conclusions are that indeed the x5 is better with an external amplifier but it is necessary to listen carefully and in good listening conditions i.e.quiet environment and that headphone/amp synergy is critical.
Edited by magicalmouse - Today at 4:10 am