ribbon tweeters

This is more complicated than you may think. The crossover needs modification and someone who really knows what they're doing needs to do it. A theoretical crossover point and curve may or may not work. I'd not do it. Get different speakers. I understand why you'd want one as my ribbon tweeters are as good as I've ever heard.

Well, the sensitivity of the ribbon would need to be a close match to that of the other drivers, or a little higher so that the crossover could be adjusted for proper balance. Also, the crossover point would need to be considered or reconsidered...

Short answer: One size does not fit all. If you just blindly pop any ribbon tweeter into any given speaker system it's going to sound like that's exactly what you did. :)

You have to redesign yr spkrs. Forget it!

Pick your ribbon and write to Bill Legall an absolute MASTER repair replacment man. If anyone an do it he can and adjust your crossover if its possible. Millerspkr@aol.com. I am not affiliated with him except I consider him a friend.
He really is known nationally and will tell you what can be done. Be prepared to pay some money he's relatively inexpensive but what you want sounds expensive,