First Tube amp suggestions

+1 for Dennis Had if going the single ended route.

I’m not an expert, but the impedance graph I found for your current speakers seems to indicate it might need a bit of power.

Look for a used Dennis Had Inspire KT88 Firebottle on audiomart sites. He hasn’t built many, but for $2k you get the performance of a $10k SET amp. He built me one last summer, it blows away my Willsenton R800i and Oldchen EL34 for texture, tone and layers of holographic imagery.

Inspire:

Hey, FYI - as a former owner of Dennis’ Cary and Inspire amps both, I would NOT strongly recommend the Inspire SET or SEP amps to someone with 90db speakers unless they were at least 8ohm nominal impedance, and only wanted to listen at lower volume levels. I ran my custom 93db speakers with Dennis’ Inspire Hot Rod KT150 amp, 10wpc and it was simply NOT enough drive for even low volume level listening. I moved to Quicksilver Mono amps and it was like somebody turned the light on the room by simply having bigger transformers and a bit more power.

Speaker matching is critical with the little mighty Inspire amps, imo.

Great amps with Inspire, yes, but I’d be running 96-100db or more speakers with the little Inspire amps. Some of the higher impedance Proac speakers, 8ohm+ do okay, but you still have to crank it up a bit much.

My audio buddy (SETDude) in FL has two Inspire amps (SEP KT88, SET 45) amps in rotation right now - he’s replacing both with a Cary SLI-80 integrated amplifier which runs 30wpc Triode into his Klipsch Hersey IVs at 96db. Told me this week it is more effortless drive than his little Inspire amps have. Worth noting for someone who is looking for an Integrated amp for 90db sensitivity speakers like the OP with Triangle speakers. Maybe some better options out there for the OP imo. Opinions vary.

Black Ice Audio:

Jumping on the bandwagon, I would also like to put in a good word after helping two friends who had 89/90db 4 & 6ohm speakers and wanted an integrated. While the parts are made overseas and final build in the USA is the case, the folks at BIA are to be commended for their service and support. It’s as close to dealing with the MFG as you can get, in the USA. If you are good with the looks of their amps, you’ll be hard pressed to find a better value for the price and sound - and if you want USA direct service. A few friends have tube rolled new production tubes in their amps too and done well. I’ve been helping friends since old Jolida days, and the new Black Ice Audio amps are another great option to consider, nice integrated amps for the $.

@tritube Looking at the impedance curve that @hilde45 provided, its obvious to me an SET will not do the job.

You need an amplifier with a low output impedance, otherwise your system will have colorations. SETs have a high output impedance. If you really want that 'artist in the room' imaging, look elsewhere.

The efficiency is also an issue for an SET. You need more power than they can provide on a budget! Since you are looking for budget tube power, I think you are better off looking in the used market, possibly for a refurbished Dynaco ST70, which can make 35 Watts/channel.

Now if you are open to replacing the speakers as well, if you really want an SET, the speaker has to be more efficient than most internet posters will have you believe. SETs really only make about 20-25% usable power; above that distortion becomes so high that the amp takes on a 'dynamic' quality and at higher power levels tends to sound loud or shouty. This latter bit is why so many SET users think their 7 Watt amp is enough power- it isn't! If they had clean power they would figure out that they are playing much higher volume levels without the system sounding loud. IOW distortion is what makes SETs sound loud. 

High efficiency speakers don't tend to be inexpensive since the magnet motor requires considerably more precision to execute and that costs money. You also sacrifice bass unless you really have a large budget or can afford subs.

That is why I think a refurbished older amp is your best bet.

Tubes4Hifi offers the VTA amps in kit or complete.  These are power amps, not integrated amps, so would require a separate preamp unless your NAD has pre-out capability. 

I added the VTA mods to my pair of Dyna 70s about 3 years ago, and have been extremely pleased, and feel I'd be remiss for not mentioning them.  I also listen primarily to folk rock, jazz, male/female vocals, and find that they drive my 89db sensitivity speakers nice in even in a large room.  A completed VTA 70 (35wpc) is just about within budget, and is definitely within reach if you're willing to solder.  

Either way, I hope you find the same magical midrange that many tube lovers do.