W/P's and a pair of Pass Labs Aleph 2 monos are a seriously sweet, but surprisingly dynamic combo, even in a large room. Aleph 2s sold for $6800/pr new, and you should be able to find a good used pr for half of that.
I crossed that bridge three years ago, when my a 3 simply couldn't push the 4 ohm woofers in my new Parsifal Encores.
A pair of Aleph 2 monos continues to provide incredible satisfaction, especially well served by an Aleph P. I'm hanging them from floor joists under each speaker, with 8' ribbons of SPM flowing back up through the baseboards. Quite stealthy, which was VERY important to Ellen....
Pair of the Aleph 2 continue to sell under $3k. Such a deal!
I've a similar system, WP5.1 and Aleph 3 in a medium sized room so I know why you like this combination. I have a number of other amps as well, when I want more power I switch to a BAT VK-200, it really integrates well with the WP's. You should give this a try, they cost about 1650 used (maybe less now that a new model is coming out from BAT), 100 WPC into 8, 200 into 4. And you won't miss the heat buildup that you are used to from the Aleph, the BAT runs very hot. The only thing is that they have balanced only inputs and you need an adaptor if you don't have a balanced pre.
I had the opportunity to borrow a friend's Aleph 3 last spring to compare to my BAT VK3i and found they share many of the same positive qualities.
Some of the differences I noticed were that the Aleph 3 did acoustic guitars better than the BAT creating a very REAL and absorbing experience. Both had very deep soundstages, but the BAT was much wider. And when it comes to power and ease of matching to a preamp, well the BAT wins that one pretty easily.
South Park is exactly right, the VK200 runs just a hair cooler than the Aleph 3, and at 1500-1600 bucks it's a great bargain.
However, if you could swing the extra cash, monoblock Aleph 2s would be pretty sweet!
In rereading your post, don't sell the Wilson's! You can get amazing sound, just up the power, they can take it. Also, the Watts are designed to be connected to the Puppy crossover, so you should not biamp them as suggested above, and the manual agrees on this point. I have heard that Krell amps work well with these speakers. I also have Counterpont SA-100 modded by Mike Elliot which works wonders, and which fills the room just as much as the BAT.
I have used this speaker as my reference for six years. It has been my experience that they need a lot of power to sound their best. I have used a Krell KSA-150, BAT VK-500 with BAT-PAK, Pass Aleph 1.2 monoblocks (Aleph 2 is a better match for some reason) and the Pass X-600 monoblocks. The best match of the bunch seems to be the X-600's. They really make this speaker sing. I have a feeling that you can't go wrong with either the Pass X-250 or X-350 either.
In my opinion, Aleph 2 should sing w/p5.1 much better in the bigger room than Aleph 3. However if you would like to add more dynamic and bass authority without sacrificing too much top-end sweetness, X-250 and X-350 could be the candidates. I used to have a pair of Aleph 2 and was trying to match them up with either w/p or Genesis G-500 (w/ 500W active woofer). I ended up chose G-500 because of its build-in active woofer providing more bass authority. I was pretty enjoying Aleph 2/G-500 combo. Aleph's are absolutely outstanding amps, but just try not to match them with low efficient speakers.
Joeabrams: Just wondering what kind of preamp that you are using right now?