Yslee,
I find Proacs responce line of speakers sound wonderful at low volumes and can play plenty loud without breaking up. I think with the quality of your equpment the would work well as the do demand good equipment. I own 1sc's and find the off axis responce to be better than most. I agree with newbee, most dynamic speakers I have heard do not play well at low volumes, proacs do. The 1sc will not give you deep bass, but do play low enough to have satisfactory full sound. With a good pair of stands they fall into your price range nicely. I have not heard the responce 1.5 but would asume they also would work well, and fit the price. The other speaker that I would strongly consider would be a pair of responce 2 or 2s now out of production but a great bargin used. They also need stands, but fit the price with. Do not be fooled by the size of the 1sc. I love them. They all favor tubes however, but worth a try at the price.
Michael