As far as I can tell, Halo Map Expander doesn't correctly expand or compress maps. In the former, it tacks on about a tenth of a megabyte of garbage, and in the latter, it probably does something similar (disc is dirty message). HMIE is the best chance we have, and until the compression's fixed, we're kind of screwed on some of the other maps.
EDIT: Shit, the version I have is a 'cygwin conversion'... it might've been broken upon compilation. I'm gonna whip out Visual Studio and try compiling it myself, to see if it works.