I made a quick visit to Stereo @ ION a couple of days ago. I ended up trying the UM Aero and Mage, using W20 as a reference point (I forgot to bring my W2). My first impression was that the universal versions of Aero and Mage sounded very similar to W3 and W4 (which I have auditioned before). I guess the number of BA drivers already dictates the sound.
The Aero was true to its name, with a thinner, more V-shaped sound and very bright treble. I am not a treble lover and some of the ess-sound was hurting my ears. So I stopped listening to the Aero after a couple of songs.
The Mage, on the other hand, was much more satisfying to listen to. The universal fit was poor and I think it affected the bass delivery. The low bass was stronger than W20 but not by much. In fact, I found the W20 bass more forward and impactful. The mids were as good as the smooth Westone's signature mids but with more detail and less roundedness. The highs were a lot cleaner and clearer. The two ends of the spectrum also extended further, making the sound more complete. However I felt that the sound was a tad "closed", with a rather narrow sound stage.
I think the Mage could be a hit for me if it had a stronger bass. For a 4BA custom with 2 bass drivers, I expected a bit more quantity and impact. Will a custom fit improve the low part of the bass significantly? Should I try the Merlin to see if a dynamic driver could do much better in the bass department? Also, if I order a Mage, is it possible to ask UM to tune up the bass a bit?