With respect to fancy tweeters, my rear surrounds are a pair of
Bohlender Graebner PD-6Ci speakers. I picked them because they use ribbon tweeters, and thus were a relatively good match to my pre-existing
VMPS 626r speakers.
The B-H speakers do have steerable tweeters and I spent a bunch of time dorking with them. They do make a difference in terms of improved imaging and better high-frequency response. It's subtle but it's real.
Note that my swanky ribbon speakers cost me pretty much what Best Buy is charging for those far more pedestrian models. If you're going to spend serious coin, you can get much better than what Best Buy has on offer.