So I got my Sony MDR-MA900 yesterday, and my impression so far is that this is a great match with the iCAN. The MA900 by itself is a spacious headphone with a unique and wide soundstage due to its unique construction. But it is the first pair of headphones that have a very wide soundstage that still benefit a lot from the iCAN's 3D effect. The other two headphones I have tried with the iCAN that are know for their spacious sound (the Beyer T1 and AKG K702) were too bright to handle the added treble energy when the 3D is turned on. So they would get too bright and edgy, and in the case of the AKGs, the sound would sometimes get an un-natural tone.
But the MA900 has a wide soundstage and yet is rolled off in the high end, so it only gets better with the 3D effect on the iCAN. And it is quite amazing how spacious and open the sound is. The instrument separation is the best I have heard yet. It is easy and effortless to follow each instrument and hear it's unique location in space. And yet the music still has a wonderful gestalt. It is just a very large gestalt! When I switch back to my ESW9s, the sound is much more compressed and can feel a bit claustrophobic until my ears adapt.
In addition, I find the bass on the Sony's to be very polite, so I mostly listen with the xBass cranked up all of the way to the high setting. The bass stays nice and clear and tight even with the full on boost, and it warms up and fills out the body of the sound nicely.
I would say these Sony headphones benefit the most from the extra features of the iCAN of all of the headphones I have tried. They are definitely a keeper, and provide a nice contrast in sound to the ESW9s. The ESW9s are more like delicious hot chocolate. Rich, sweet, fun and somehow warming to the soul. The MA900s are more like the clearest, cleanest cold spring water: the sound is so realistic and open and spacious that it leaves a totally clean and empty aftertaste which is totally refreshing.
The Sony's are available at a very good price on Ebay for another day or so: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=330986774496&ssPageName=ADME:X:RTQ:US:1123