Ring radiator tweeters - the future?

Gmood-- y're using a wide-range driver. You have tweeter response anyway.
Out of curiosity, how do you cope with the 4kHz bump in yr response (I'm referring to the "sizzle" you mention)? Note, I'm not knocking yr spkr --just asking.

BTW, the Vifa & Scan rings are not necessarily the problem: their implementation is usually the problem.

Eldartford sez:

My idea is to exploit the extended range capability by using a FR to cover the range from 100 Hz to 8KHz or so, with a SW below and a tweeter above

You'll enjoy yourself immensely on that one! I expect you'll find that the tricky part is marrying the woof to the FR. IF you can hi-pass the FR & leave it alone thereafter, it's a bonus.
You're lucky in that you're already used to having (seeing) obtrusive panels in yr room... Cheers