Amplifier sensitive... I can believe that. I recently moved and had a Yamaha black faced nineties receiver.... medium sized, fifty watts... hooked up to them as a stop gap and the combination sounded terrible... I mean terrible, thinking placement, something... wouldn't listen to it. I had a Sony STR 7045 lying around so out of boredom I wired it to the Altecs..... and my goodness, what a difference. I also have a Marantz 2235 which I then also tried... and what do you know, it sounded even better, marginally better but better... rich and full. Not stopping there, I subbed an Amp 200 I had acquired for the power amp, using the Marantz pre out... it sounded like the Yamaha.. I even drove it with the headphone jack thinking maybe impedance loading, something like that... exactly the same as with the pre out. I then subbed a QSC GX3, of which I have two... long story... first with the pre outs, then with the headphone jack driving it... and while it was much better... much better... it still wasn't warm... like with the Marantz alone. I spend a few years doing bench work at a high end repair shop and have many pieces for comparison after repair or service, and some units do sound quite a bit better than others... at least on my bench speakers which were good twelve inch three way Infinities... and among those that had a characteristic sweet, warm sound were, generally, Sansui amps and receivers from the 2000... 5000 series through the eighties G series, of course their AU amps, earlier Fisher Transistor, TX series, and of course their tube receivers, thinking the 500 C, and the Marantz stuff. A few others too but those always stuck out. It is interesting to know that Altec voiced their speakers using the manufacturers amps you mentioned. Altec used to be in Anaheim California not that far from Soundcraftesman. As I'm sure you know, the 19s don't need much power in a living room to sound big but if you feed them big they will continue to use it.