That sounds ok to me at the output side. The speaker would be connected between the two positive output terminals of the amp (I think, although I'm not certain offhand, that you would want to use the 16 ohm taps if you have 8 ohm speakers), and the two negative output terminals of the amp would be left unconnected (they are tied together and to signal ground internally).
On the input side, I think you are saying that you would take your xlr source (transformer or preamp), and construct a cable that ran xlr pin 2 to the center pin of an rca plug, and xlr pin 1 to the ground of that rca plug, and ran xlr pin 3 to the center pin of another rca plug and xlr pin 1 to the ground of that second rca plug. The two rca plugs would then plug into the amp's two rca inputs. Correct?
Or are you saying that you would replace the rca inputs on the amp with an xlr connector that you would install, with pin 1 wired to amp ground, pin 2 to the single-ended signal path of one channel (wherever the center pin of the rca had been wired to), and pin 3 to the single-ended signal path of the other channel?
I think that everything would function either way, but I'm not sure that you would gain all that much in terms of noise rejection, especially if you don't replace the rca input connectors. Balanced inputs reject noise that is present equally on both polarities, but with the two polarities being physically branched off I'm not sure that noise pickup would be really equal. You will gain a lot of power, though.
Regards,
-- Al