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
My Vandersteen speakers have an additional rear firing tweeter that is adjustable/off.   Using the tweeter, it sounds bigger, but the pinpoint imaging is gone. Off for me is preferred.
String - Me 2, flat to something like 30 khz, 100% out of phase distortion that some find attractive in an overly dead room, or a standup cocktail party…..no sweet spot there….
My primary speakers for years in my 2.1 channel system were a pair of Voight Towers with Fostex FE-206 full range drivers. I added a Fostex FT17H Horn super tweeter to the speaker just to see if I could expand the soundstage a little more. I had already added a small Martin Logan sub that worked really well with the FE206s. I followed the Fostex recommendation and only added a 1.0uf capacitor ahead of the FT17H. Much to my surprise, adding the tweeter did make a difference. The best way I can describe the change is the soundstage ceiling (I see it as a sound field bubble - I know that sounds weird) was higher or more expansive in the room. That sound field bubble was larger and made the previous field seem cramped by comparison. 

I no longer use the speakers. My son and his roommates are enjoying them at university now. They aren't focused on quality of the sound, but they love how loud they can play!

Cheers!
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