'Box' speaker that reproduces the piano well.

ATC do piano quite well. SCM 40 or 20 should be within reach of your budget. The owner/founder of ATC is an electrical engineer with a Masters degree in Acoustic science and has been gigging jazz piano for 40 years (since 17 years old)

 "Bösendorfer/Brodmann is the best I've had or heard for piano. "
There should really be a smiley appended to this.

There aren't many speakers upward of 30K that do piano well. 

I’m talking about their speakers. I should have specified considering they make pianos and my post might have come off sounding like a smart a*s!

I was referring to their speakers. ;-)

I am always thrilled at the sound of piano on my Harbeth C7ES3s. 

FWIW, here's an old exchange about the Bösendorfer/Brodmann:
https://www.stereophile.com/content/bosendorfer-loudspeaker-1

This is the Internet.

Agree with ATC, but your 35 wpc amp would probably not have enough juice to drive them properly so you'd likely be limited to using your ss amp.  Best of luck. 

Zu Druid Mk IV with Densen DM-10 MkII, First Watt F5, Leben CS-300. 

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!