I will echo Jim’s @tomic601 recommendation of the Vandersteen mono’s. No doubt an obvious system symmetry approach.
But, if more than you want to ‘pony up’, I recently added a pair of used but excellant Belles MB-200 mono blocks in my system driving my Treo’s. Belles just knows how to make everything he makes musical. Also, a great fit with my ‘new’ Belles Aria Signature preamp. Happy camper.