Need at least 900wpc in 4ohm

High sensitivity speakers make low sensitivity speaks sound like they have a wet blanket over them.

Until you feed them with 900 Watts. :)

I love Triode's AND Jim_swantko's comments. I've tried both, having had several different SET amps in my systems the last maybe-10 years, driving hi-efficiency (more than 100dB) linearrays. As the rest of my system increased in resolution, so I wanted higher-rez speakers. I quickly determined that I had neither the skills not determination to build them myself, and bought a pair of Audio Physic Avanti IIIs which were fairly quickly succeeded by the best speakers systems I've EVER hear, Vandersteen 5As.

I tried biamping them with a few different combinations of small amps but finally bought a pair of McCormack DNA-750s. WOW did my system 'come to life'. Altho I do not listen at high levels, these HIGH-power amps brought a sense of ease...effortlessness...that my system never had. Tccaux, I suggest you read Peter Moncrieff's review of the DNA-500...
http://www.iar-80.com/page5.html
...to get some sense of the McCormack sounds and then understand that the '750 is a further refinement (by the manufacturer, conrad-johnson) of the 2 significant principles Steve McCormack used--Distributed Node Amplification (meaning placing significant powersupply capacitance immediately adjacent to the output transistor) and fully push-pull, differential amplification (meaning that half the amp is pushing while the other half is pulling), and then buy a pair. I'm confident you will NOT be disappointed.
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The Snell AIII was a good speaker in its day. It was about the only thing out there that competed with the Fulton Premiere systems. But that was 1984. Snell made a speaker call the B that I found preferable to the AIII- easier to drive and more detailed (still went to 22Hz).

Since the time of the B, there have been a lot of other speakers that have appeared that are easy contenders. If you want something on the scale of a speaker like that, with a reasonable price that is also easy to drive, check out the Audiokinesis Dreammaker, which got a Golden Ear award a few years back. I would take if over a set of AIIIs in a heartbeat- especially if you have a larger room- you need the efficiency.

The reason you need the efficiency is the simple fact that there are no particularly musical amplifiers that also have power in excess of 500 watts. Sure, there is lots of stuff that sounds like good HiFi, but if you want it to sound like real music, that amp does not exist in those power levels, tube or transistor. So you have to get the efficiency going. You might also consider that fact that if you really push a +500 watt amp into those Snells, you will toast them but before that they will be highly compressed.

Sorry to break it to you this way but there is no way to change the laws of physics. If you go with a smaller room you will have a lot more option with that speaker. Of course, if you only plan to play at lower volume levels maybe you will be OK. Personal preference *does* play a role in that regard.

I disagree with Atmasphere's assertion that there are no particularly musical amplifiers that provide in excess of 500 Watts into a given speaker.

Try a pair of Cary 500 MB; 1,000 watts into 4 ohms. They will drive just about anything and not break a sweat... Closest thing to a high powered tube amp that I have heard... They sound great, smooth, and very dynamic. They are excellent mono-blocks for tough load speakers or speakers that demand lots of current (like Maggies). Can pick up a used set for around $4k.