I have a Marantz NR 1403 with Audyssey MultEQ, Dynamic EQ, Dynamic Volume. The receiver only puts out 50 watts per channel and my front floor standing polk tsi 400's require 20-200w. I would like the add a two channel amp to power just these two speakers in my 5.1 system. Will adding an amplifier like Emotiva UPA-200 2-Channel Amplifier mess up my Audyssey calibration?
No - an external amp won't 'mess Audyssey up' but it would be prudent to run the calibration level again as the external amp's gain may be different from the AVR amps' gain and this could throw the relative levels of the speakers off.
What are you using as a centre channel speaker? It may be worth considering the XPA-3 to power the R, L & C. The centre channel is the most important in a 5.1 system. Just a thought.
I believe his receiver only has preouts for FR/FL channels so that idea is a no go.