Hi Duomike,
rock and roll! It is one of the joys of a good horn. Incredibly easy to hit high SPLs with no stress or compression or strain.
I have a db meter and there is no problem hitting 100db. Sometimes you dont even notice how loud it is until you try to speak.
I have yet to bring my volume up into the low 10s or closer to 0 (fully open), Anywhere near 20 on the volume read out (in the 2v output setting) is very loud and reasonable head banging or gig level.
Remember the speaker is 110db/watt. Obviously there is a fall off with distance, but I sit quite close. 4 meters or so.
Depending on the recording level of the material you can gain or loose some power. I have headroom though. Not forgetting 500w of active sub.
So far I have not noticed any issues sonically when pushed, and as I said I had all sorts of amp on the Trio, from 2 watts up to 1000 (Well 1000w @ 4ohms). I hand on heart can say the power was of little or no consequence, but the presentation was another ball game.
My buddy has a Duo with Welbourne Labs 45 monos and I have never heard him complain about SPL, far from it. He ran all sorts of SS amps, including the AG ones too.
It is said 85db and above is dangerous and causes damage to the ear. Sustained 100db pretty bad. Although it sounds good!
I have spent much time standing next to drum kits and giant rigs and I am still here, although why does every recording have ringing bells on it... even when it has finished playing?!
I would suggest trying to borrow a 45 based amp and see how you get on (make sure you use a modern tube).
I had the type of sound you get from your millenium for years. I did all those kind of amps. Halcro etc. I had amazing sound. But I hate to say with the 45 something was just right. I am sure there are a few of you who have seen my threads attacking the rubbish aspects of tube amps and tube preamps I have had. They were mainly huge amps with many tubes. But here I am with a bloody 2 watt SET! I was really anti tube and I still am. I just cant deny the quality of the 45 on high sensitivity.
I would like to have one or 2 aspects of that SS or digital sound back, but not at the expense of what I have. So far the Yammy is the Goldilocks amp that was just right over all.