While i have NO idea as to what type of music you listen to, the volume levels that you want to achieve, the listening distance that you want to achieve them at, the tonal balance of the source and speakers, etc.. I will say that you need a LOT of power to do things "right" under the circumstances that you've outlined.
The room is QUITE large, the speakers are not very efficient and they present a sligthly lower than average impedance to deal with. Whether or not they are a benign load or reactive would be something that you should find out, as this could further stress the amp(s) and possibly remove some of the candidates from your list.
If you want to play your music loudly, do it cleanly and have authority at those levels, you better look for something that is AT LEAST ( at the very minimum ) 400 wpc @ 4 ohms with decent dynamic headroom. As to why i say this, let me give you some background.
I have speakers of the same sensitivity but are rated at 4 ohms nominally. In a room that is MUCH smaller ( 18 x 15 x 9 ), this took an amplifier that was rated to do 600 wpc @ 4 ( actually clips at 760 wpc ) to achieve the results i was looking for. This amp sounded cleaner at high volumes than when i had two different amps passively biamped but still ran out of steam at about the same SPL. The two passively biamped units worked out to a rating of 900 wpc @ 4, which they would easily do. Just for sake of clarity, i had 400+ wpc for the mids and highs and 500+ for the bottom end. While the two passively biamped amps had better bottom end than the solo amp of different make, the smaller solo amp was cleaner throughout the frequency range above that at any power level.
Even with as much juice as i had on hand with either of those combo's, i could hear the amps starting to stretch and smear on sustained peaks. I ended up using an amp that is rated at ( and easily does ) 1200 wpc @ 4 to do the job that i was looking for with these specific speakers. If anyone would have told me that i would have needed this much power to make them sing, i would have NEVER bought them.
You might be able to get away with a LOT less power than that if you don't want to listen loud, your musical tastes are mellower and have a lower average power demand and your speakers don't go into dynamic compression as they are pushed. Otherwise, you may soon find out that "more IS better" when it comes to wattage.
This experience alone taught me a LOT about what it takes to do the job with low efficiency speakers. Bottom line: If you wanna raise the roof while maintaining good sound quality and not go bankrupt, start off with high efficiency speakers. Your choices on amps are MUCH more flexible and potentially less costly. Sean
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