Since you use the 340 for mains, it would seem to make more sense to modify those, no? The surround speakers are not very critical compared to the L, C and R. And for the vast majority of music, only the L and R are important.
As for ME doing any work on them, well, maybe middle of 2009. I am neck deep in trying to get projects done that were due 2 months ago. I just do that stuff in my spare time, and I don't exactly have a sufficient shop/work area to do the stuff efficiently. At this rate, I won't get my new main speakers done for myself until the end of 2009, if I'm lucky....
-Chris