Super tweeter for FullRange Driver


I have a pair of Audio Nirvana 15in Alinco Classics that I just got done getting into cabinets. After some listening impressions, I've realized I cant live with the high frequency response these things put out by themselves. They only go to about 15k hz. and it's made music lose its sparkle and sense of space and spacial cues. I was thinking of buying a pair of Fostek T90As and pointing them at the ceiling for a more even dispersion and better integration with the Audio Nirvana driver. My main question is what  capacitor volume would you suggest? Where in the frequency response would you crossover to the tweeter? Would wiring the 8ohm tweeter and the 8ohm Audio Nirvana in parallel make me need to change my amp(Audio Note Kit 1 300b Set) from 8ohm to 4ohms? Any other brands of tweeters recommended for a fullrange driver that is around 96bd efficent? Sorry for all the questions, incredibly new to trying to implement crossovers with full rangers. If this sounds like a bad idea. Please speak up. 
akwilson501
the Fostex is a good choice. I’ve used the Heil AMT 1D tweeters with great results as well
akwilson501
After some listening impressions, I’ve realized I cant live with the high frequency response these things put out by themselves. They only go to about 15k hz. and it’s made music lose its sparkle and sense of space and spacial cues.

If you want the very best. Get a pair of these Plasma tweeters that I’ve got, no mass. Highs just dance in front of you like firefly’s. They’ll sit on top of your Audio Nirvana Classics and look the part too.

Adjustable level, and can go down to 5khz and reach up to a staggering 100khz!!!!!.
https://www.ebay.com.au/itm/Magnat-Plasma-MP-02-ion-tweeter-massless-air-plasma-speaker-Plasmahochtoner/282700838884?hash=item41d24877e4:g:yJkAAOSwTmtZ6PwI
He's dreaming on the price, I'd ask around $2.5k for mine.
Cheers George

This discussion remain me how is different the taste,  i dont want to tell the famous brands on the market now which use one full range driver
with double cones  , main cone and whizzer, which play a tweeter-super tweeter role, and say the sound is beatifically, Conclusion-   some like piece a paper as supertweeter , some need plazma . sorry for my english