l'd concur with James and Lee that Adobe Acrobat PDF format Reports are definitely prefered where the audience is:
-of considerable size
-of varying skill base (ie, understanding use of MSP software)
-unlikely to have a copy of MSP software
Working on similarly large projects l too have found exactly the same issues / problems with electronic delivery to be "problematic" where other PMgt teams used an alternate brand of PMgt software [converters are not always available], etc.
Adobe PDF format is universally used, it comes with the free viewer, and (most importantly) the document creator can control document layout via the internal "security control" features of the Adobe software.
Note: Where the audience are seasoned PMgrs with copies of MSP then electronic delivery is less problematic.
You could also consider use of the new MSP ProjectCentral functionality though many comments in other MSP Discussion Forums appear to indicate stability of MSP ProjectCentral itself is still "problematic" [maybe that is a subject for another thread].
Rgds - Dcn
PS - users looking for answers to highly technical queries ought to visit the MS-TechNet Discussion Forums as these are an excellent resource for experienced users of MSP software.