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
I don’t understand why most people do 1st order crossover for super tweeters.
The only answer that comes to my mind - the 3rd, 4th order is too difficult to implement for average audiophile.

My experience shows a huge advantage of 4th order crossover over 1st order.
It is like to upgrade the speakers to at least to 2 times more expensive pair!

The difference is:
Mid range is much more smooth, less harsh and much more detailed.
Much better soundstage - bigger, deeper, more clear location of instruments.
Better separation and low level details.
A lot of high frequency details that wasn’t exist with 1st order crossover.

The important note. Whatever order of crossover is used - forward firing super tweeters have to be aligned with other speakers.

Regards,
Alex.
Here are examples for comparison:

Fostex T90a with 1st order crossover:
https://youtu.be/vTOK7lMPAW4
Fostex T90a with 4th order crossover:
https://youtu.be/o001l1f_FDw

Fostex T90a with 1st order crossover:
https://youtu.be/ZfvWxALxvw8
Fostex T90a with 4th order crossover:
https://youtu.be/R-xkKuGEp78