I will agree only in part here. I am able to detect a change in sound stage by moving the cups around. But there is just nothing about the treble that sounds bright no matter where I put them.
I may borrow a friends ican and give it another listen. I did not have the ma900 when I auditioned the ican can previously. Maybe it deserves a second look/listen.
Even if they do not ever sound overly bright, does the tone shift downward when you move them forward? That might be a disadvantage in your setup, especially since the MA900s are normally rolled off in the high frequencies. But I definitely hear a warmer tone overall when the headphones are forward and a brighter tone when they are further back.
I will be curious what you think if you do try them with the iCAN. Everyone's hearing is so different, but you might enjoy the combination as much as I do. And if you are willing to go way out on a limb (or at least $50 out on a limb), you could try the TDS202 even with your current setup:
I have found that the TDS can sound great in certain setups and not so great in others, so this is definitely one of those YMMV suggestions.