'Box' speaker that reproduces the piano well.

Genesis Vs do a wonderful job with piano, are well under your budget, and I suspect would work with either amp.  For a different presentation, the Audio Physic Avanti IIIs are nice as well.  You can also occasionally find Verity Parsifal Encore's in your price range, which I would also highly recommend if you are interested in an accurate rendition of the piano.  However, for the latter two speakers, I am not sure how they would work with your 35 w/ch tube amp -it really depends on the amp.  For example, the Vac Renaissance 35's should work very well with either (depending on room volume and other system factors), but other low powered tube amps may not be the best choice.

Avanti1960 has a good point. Smaller speakers or monitors will improve the sound. Piano's to me sound boxy. Smaller speakers don't have all the cabinet resonance of large speakers so they are cleaner sounding.

Similar to James, when I read the question I thought of Brodmann. My memory is fuzzy but the company’s demo of the Festival and VC lines included their music, all of it piano, both contemporary with vocals and classical. In light of the well braced, half-dead sounding and still colored speakers, I thought the Brodmann’s were awesome that day. Vocals and piano were full sounding and dramatic. Imaging was surprisingly normal as I recall. Maybe they are one-trick ponies and maybe they make all pianos sound like a Brodmann model. I don’t know. I think ATC is a good suggestion as well.

Klipsch La Scala!