Whats the difference between using the balanced inputs VS the RCA inputs?
In this case, it makes absolutely no difference whatsoever.
The XPA-5/XPA-2 will simply convert those balanced signals back to regular unbalanced signal once the signals enter the amps.
In a "fully balanced" amp, the balanced signals remain fully balanced even once the signals enter the amps. In a fully balanced amp, you theoretically gain improved SNR & Crosstalk. However, in practical everyday world application, you will not notice any difference.
The balanced amps are supposed to prevent the ground hum noise. However, they may still not prevent the ground hum (caused by cable/satellit lines) and you will still need a ground loop isolator to stop the ground hum.