Having spent an extended amount of time listening to these quads, I think it's time to offer extended impressions.
When I first got them back, after having listened to the U curve signature of the M50 for so long, I was initially taken aback by the quads' relative lack of treble sparkle. I felt as if the music was not 'crisp' enough and the highs were getting rolled off, though they were extremely comfortable to listen to for long periods of time. The highs never got in the way of the entire song. After I did some EQ with a peak at 7k, I was able to achieve my preferred sound signature. Now the quads offer crisp highs along with very substantial and extended lows.
The bass of these guys may be off-putting to some, but I think they have enough bass to satisfy almost any basshead. The sub-bass is present, and makes itself known where the song requires it. The mid-bass is very obviously present and offers excellent PRaT. I did not feel the bass as a whole to significantly detract from the mids and highs, because they are 'separate' from the rendering of the latter.
Soundstage is slightly better than a typical IEM (W4 is slightly more narrow), and if imaged, is about one palm's distance from my head, forming a hemisphere on the front of the head.
I think the quads should be EQ-ed in order to let their full potential shine. That was what I felt when I opened up the highs using the eq. Suddenly everything was clearer and I was hearing cymbals again.