There are many ways to improve RS-4000s, I just did it the counterintuitive way, Pioneer CS-06 8", CTS mids (to be replaced with the original Infinitys) and Foster/Radio Shack square plastic tweeters. Then I pulled the Infinity badges and glued Pioneer on to match my CS-K835s. But like I said, the woofers were totally spent and I had no EMITs. I have seriously considered putting Polk Audio domes in place of the Fosters, like Monitor 10t or similar. The crossovers are stock and I don't run anything that will pull the impedence way out of line.
I've had smaller Infinity tweeters but they are in use in other speakers.
As for the Advents, you can replace the woofer all you want, they are just too small for loads over 25 watts. This is from personal experience having owned them.