used Integrated tube amp under $1500 for Klipsch Cornwall III's?

My 1st question would be, what are you not liking about the Forte 111s ?, although, they are not optimum in corners because of the rear facing passives, so that could be it. If corner placement is desirable, get a pair of 2nd hand Lascalas, as they are in another league over both the Forte and Cornwall ( imo, ime ). Modifications galore for Lascala. Stay away from flea watt amps at this time ( 2-3 watts ), as you need damping to control those woofers ( any of them ). Have you heard a tube amp on the Fortes ? Why have a piano in between the speakers ? if ( 1 ), it is never used, and ( 2 ) you are needing space. BTW, I do not recommend corner placement, if you can help it. Enjoy the journey. MrD.

I would place it on the piano.  You run the risk of the tubes picking up the vibrations from the speakers and feeding back when on the speaker (microphony).  Some amps are more susceptible to this than others.  

I have used my Decware mini torii 4 wpc with my Klipsch Quartets and they rock, almost too loud at times.  The decware is very well built. Not flashy finish but not cheap.
I also used a Grommes PHI-26 2/6 watt with the Klipsch and sounded great.

the piano is for show
its not that I don't like the fortes but I want to experiment, a pair of mint  used cornwalls became available at a good price

interesting that many people are recommedning both for and against low powered set's
at some point i will try both

Decware as I mentioned, and others on this thread, is excellent sounding gear. It may look utilitarian but far from cheap. If great sound, synergy with your speakers, pickup the phone and speak with builder/designer, and lifetime warranty - may not be your cup of ☕️