My X3 is a little longer and thinner than my DX50. My DX50 has a bit more open sound than the X3. With everything taken into account, I think the X3 and the DX50 are equal with sound. I might be inclined to recommend the DX50 because it looks nicer, has better ergonomics (even though I'm not a big fan of touch screen interfaces) and because the line-out on the DX50 bypasses the volume control.
DX50 line out is still volume adjustable, but you're still bypassing the internal amp section.
Edited by H20Fidelity - 10/16/13 at 3:04am