which speaker to buy

First, I am a Tekton owner. I have a set of towers that I like very much. At one time I pushed many others towards Eric's products. I no longer do that. I no longer recommend Tekton. Not for a purchase new anyway. 
Though the Tekton speakers are quite good for the money I no longer feel that they are a good company to do business with. It does not matter how good your product is if you can not complete orders. Many have waited months (or more) for just the grills that were purchased with the original order. Some orders for speakers without grills are taking 6 months or more to be delivered. Emails are not responded to and phone calls go unreturned. It seems between his IRL project, racing interest and life in general Eric is no longer able to keep up.
It doesn't matter how good a product is if your company is not there to support it. 
Here's where the "not for a new purchase anyway" part comes in. 
On the used market a 1 to 2 year old Tekton brings roughly 60% to 70% of original purchase price. I have seen them for less. I regularly watch the market because I WILL purchase used. You just have to decide exactly which one you want and watch for it. 

IF you really want to duplicate Zep level SPL then you need pro sound reinforcement drivers and mid / HF horns. You could look to the Dead and wall of sound and build it modular. I advise JBL pro level drivers. Budget for hearing aids.

Just because he can bridge doesn't mean he should.  For efficient speakers like Klipsch, he'll only be using a few watts at most before driving them to hearing damaging levels.  It's good to have that extra headroom for dynamics, but bridging them is a dumb idea.  If he goes for Klipsch, some of the more recent (III or IV) Heritage speakers would be the way to go in my opinion.  Klipsch will do loud and will rock out, but they are not the most refined speakers out there and may play loud, but may not sound that great when they're really loud.  I have owned and listened to a lot of Klipsch speakers and almost all of them hurt my ears at loud volumes.  I had a pair of KLF-30s that I really liked but those are hard to find and they have issues with the cabinets ringing and falling apart.

Legacy Audio as mentioned makes more refined speakers than Klipsch that can play very loud.  I had some Focus 20/20s and those were beasts and sounded noticeably better than the KLF-30s at high volumes.  I sold them eventually because they were just overkill for my space.  They were hard to let go.

I was considering some Zu Audio speakers recently but decided against it.  I talked to a number of people about them and the consensus was that they do very well with low watt SET amps but aren't necessarily a good match with higher powered amps (I have 180 WPC tube monoblocks).  I did not hear them and have no direct experience, so take that for what it's worth.  

The Tektons look "interesting".  I'll just leave it at that.  

If he already likes the Klipsch sound, then he should listen to a pair of La Scala's. 

If your son wants his music that loud, then you're going in the totally wrong direction.  Home audio hi-fi speakers can play only so loud.   What your son needs is pro sound gear, which is engineered to play at much higher sound levels.  If you're listening to it that loud, fine detail and nuance are totally lost.

To my ear, some of the very most musical pro sound loudspeakers are those sold by Bag End.  Look  for a pro sound dealer at their website.   The amps you currently  have should work fine.  Pro sound gear is typically more efficient than home audio.  But if he really has to have more power, then he should go to the Musician's Friend website and get one of the big pro amps they have there.

All this will cost much, much less than McIntosh and other audiophile oriented gear and do a better job for this application.