Realistically, your Cronus Magnum Probably only puts out 10, 15, 20 watts per channel at best over the range of human hearing and still maintain a maximum distortion level below 1% to 3%. Don't believe the 100 watts per channel hype. That's just the way it is with tube amps. It still will easily drive many of the moderately efficient speakers out there.
As @celtic66 suggested the ATC SCM40, a bit out of your price range though but deals can be had if you can find a retailer that carries them. They are wonderfully made mostly by hand except for the enclosures which are outsourced from a local vendor. The drivers have enormous magnet structures with underslung voice coils and all their parts are meticulously fabricated and assemble by hand.
Since it's a sealed enclosure the bass roll off is relatively slow and will still have prodigious output below it's -6dB 48Hz specification. In addition, it will present a fairly benign load to your tube amp because that tends to be the nature of acoustic suspension speakers. Something to consider.
As others have mentioned, ProAcs, Revels, Dynaudios, which tend to be on the brighter side and Klipsch's though incredibly efficient are not necessary unless you're into headbanging or something. I think the Wharfedales, MoFi, and Sonus Faber are good recommendations and worth seeking out. You may even find a speaker among their lines well below your maximum of $5000.