I use ProAc Reponse 2.5's, which I originally auditioned with the Premier 11a, and I'm now driving with Premier 12's. I've had this system for about 2 years and I've been very pleased with the sound. Its extremely musical, produces a huge soundstage, and is easy to listen to for long periods.
Personally, I'm a big fan of the ProAc sound, and think that there's a certain magic in this combination that I haven't found with other systems. However, I think that you'll find that the Premier 11 can sound good with a great many speakers. It has a very sweet, lively, warm sound that works well pretty much across the board. I know that there is at least one agon'er that mates his 11a with the smaller Thiel speakers and likes the results quite a bit. If you're in a position to visit a few audio stores and audition speakers, it would be worth your while to take the amp (and your preamp) with you and see how things sound. I'm sure you'll have no problem finding a combination that speaks to you.
In any case, enjoy the search...
Cheers, Ken