Tubes with Infinity IRS Betas

You said it yourself "many moons ago"...let’s say customer A has a nice used pair of Beta’s, a fully refurbed Threshold S/500 Series II (of which you’re very familiar) and a 2nd hand ARC Reference 110 with new NOS tubes, where are you going to put the tube amp?

Wouldn’t change anything, if fact back then our hearing was far more acute, still remain the same, as that downward sliding impedance curve
3ohm@150hz
2.5ohm@700hz
1.5ohm @3khz
1ohm@20khz
This would still knock the HF out of the tube amps, on the Threshold s/500 things will remain flat out to 20khz.
And the Ref110 should cope still with the bass tower impedance, it doesn’t go below 5ohms on the Stereophile graph.

Cheers George

Yeah, cheers George...

Not so much coin to put a Threshold into the mix
for grins.....

I have had a set of IRS Betas for just over 10 years now, and still have my original pair of Quantum 5s. In the past I have also had Kappa 8s, Kappa 9s and IRS Delta's.To power them properly & safely, I personally have had good results with the older vintage Threshold amps, S300 MKII, S350e & S500e.I have also had good results with modified Halfer amps as well, some moderately modified stereo DH200 and DH220s, and more recently a pair of extensively modded mono Hafler DH200s with custom driver boards.With the Betas I like to use the modded mono Haflers on the mid-high towers and the Threshold S350e on the bass towers, and that setup has power to spare and is the best sounding combination so far.Last year I picked up a pair of Doge Audio tube mono amps, and they do a a nice job on the mid high towers in class A mode. They do run very hot though, definitely need to make room for them to breathe.For the Haflers, I usually do not push the idle current, so they run warm but are not outrageous power consumers.The only thing I regret is not having a big enough room to do the Betas justice.Even so when people hear them for the first time they are blown away.

Back when I owned Infinity RSIIa, (they had three EMIM, three EMIT, two woofers below) I powered them with a Carver. (1985)
I remember he day I played The aria Figaro from The Barber of Seville,  for the entire neighborhood... ( someone was playing very loud music on Saturday mornings a block away.. And on this Summer Saturday I want whomever that was to hear what I was playing.. Opened the windows, put in earplugs and blasted the entire aria so folks two blocks away could hear it clearly.                 
No problem.               
Another time a next door neighbor was annoying me. So I cued up Some hard rock, cranked it up and let it rip. suddenly.               
A few days later the manager, who lived directly above me, told me she was startled out of sleep first thinking a truck had hit the building.... We both laughed.                                  
That was back when EVERYONE was way more laid back...