Loudspeakers that go LOUD?

I recently finished off a basement room that is 24.5' x 22.5' x 8'. My beloved Tyler Linbrook Monitor Signatures sound as wonderful as ever there provided I reign in the volume control somewhat, otherwise the SEAS Excel 7" drivers start to protest. I'd really like to find some speakers that wont give up too much in quality, especially in the areas of treble refinement and in imaging, but will play loud without strain. The few horn systems I've heard sounded peaky in the treble to me, but perhaps there are some which don't. Suggestions will be gratefully received.

Parameters: For music I am into classical, opera, female vocalists like Eva Cassidy and Jennifer Warnes, movie sound tracks, shows, golden oldies, but no heavy rock or metal. Power is via a 50 watt/channel tube amp but that could be changed out. Budget: on the order of up to $3K new or used.