An update about the m903. I really enjoy it with two pairs of headphones:
1.) Philips SBC HP910
These are a fun can to listen to. They are nothing special to most people, but to me they produce a completely fatigue-free spectrum of listening bliss. Tyll and I did some tests a while back and he was not impressed, but he really did more testing than listening. You have to amp them or you just leave yourself in the line of audible fire.
2.) Denon AH-D2000
The Denon AH-D2000 is already incredibly flat in the frequency domain which is one reason I like it. In addition the m903 is also very flat. Combined the two really complete each other. The only thing I found missing from the AH-D2000 + Grace m903 combo is the lack of resolution while listening to binaural recordings. For some reason my Grado's reign supreme there.
The Ultra Desktop + AH-D2000 was a bit too boomy for my taste. In all I really enjoy the m903 and do not plan on replacing or upgrading any time soon. The only other can I would consider would be the LCD-2 as it sounds a tad better than then AH-D2000. I tested myriad other headphones including T1, T5, HD-800, and none sounded as nice as the AH-D2000 through the grace to my ears.
Perhaps if you find your AH-D2000's too bassy the m903 will mellow the bass out.