It looks like the higher pitched sounds on MM1 and MM8 were fixed in this version. When I look around for change logs about this I just see ones for the PS2 and Gamecube versions, so I am not 100% certain about it.
Anyone know where a list is of the defects in the xbox version?
This Wiki article on it has quite a bit of information on all the versions and the changes. According to it xbox is one of the best versions but once emulated on the xbox360 it degrades the quality dramatically. The Xbox version has the most extra features followed by the PS2.
http://en.wikipedia.org/wiki/Mega_Man_Anniversary_Collection --- Mass confusion can change how a civilization operates. Changing the world requires the same chaos.