IMO UE900 is technically better than W4 because
it has better bandwidth, both on par in treble extension but bass extension is better on the UE900
Both have a similar resonant peak in the treble but the W4's is worse, UE900's is fairly small.
W4 has more midbass, imo it makes it more flawed as it's a bit too much but this one is up for debate. UE900's bass is tunable to some extent.
imaging is similar as is soundstage.
Edited by Inks - 2/20/13 at 7:30pm