There is a member here with a set of Avalon Acoustic Eclipse who put a Eidolon midrange in place of the tweeter. I spoke to him one evening and he seemed truely happy with the mod, I would have tried it if I didn't have to cut larger holes in the cabinets. I am not sure if something like that would work for you, but there is a chance. That being said I am going to have to agree with the statements made above, I would not recomend upgrading those speakers in particular, money could be spent in other places having a better effect. Check out www.zalytron.com I know they can do everything you want to get done, they tend to help a lot of DIY'ers but I am sure they can upgrade anything, all it takes is $$$. Good luck
~Tim
~Tim