That is a tuffy!

How about attaching them to the outer most sides of the corner cabinet, or ceiling area above and to each side of the cabinet.
They are obviously waaaaaay far apart now......Maybe one just above and to the right of the piano and the other same height between the first and second pane of glass, using those nice mounting brackets.
I wouldn't give up......there must be the right spot somewhere.......................Pat

Axiom Denon Paradigm SVS