Just got a new power amp

At the risk of dragging out the "balanced" discussion, and for what it's worth, my statement about the S300 being fully balanced came directly from a conversation with PS Audio and from their literature.  They state the S300 is a dual mono amp with separate power supplies (which I can confirm because I had to fix it when I bought it) and, I quote from the 'features' list, "XLR 'True' Balanced Input".  Is it just advertising speak, maybe...

Here is the link to their product literature (same link that @cleeds posted):

https://www.psaudio.com/products/stellar-s300-power-amplifier?srsltid=AfmBOorSOah2MfUtjhdiEtDofo_33rZPxhQjskOADreDpaqznZuPQ-7S

Thought the conscience was to always use XLR, they have a much lower noise floor, carry less noise, have less signal loss, of course higher gain. 

Why would you not? Lowering the noise floor is always an improvement.  

If there is an audible difference, something is defective.

@kr4 I'd put it the other way 'round. We audiophiles are very used to hearing interconnect cable differences. But recording engineers, who use balanced lines in a studio, are not. When the balanced line system is set up properly (as usually seen in a studio) the 'sound' of different interconnect cables goes away. 

Having done many auditions of this difference over the last 40 years I can say that RCAs usually don't sound as good as a result and nothing is defective; this providing that the balanced line equipment actually supports the balanced standards (such as AES48). 

"Fully Balanced Amplifier" means that balanced input section (instrumentation amp or transformer) is followed by two separate amplifiers, each driving one speaker terminal.

@kijanki Could you explain what is meant by 'two separate amplifiers'? Do you mean two single-ended amplifier circuits or two push pull amplifier circuits, or something else?

@atmasphere   "Fully Balanced Amplifier" is in my opinion an amplifier that consists of true balanced input stage, like transformer or instrumentation amp, followed by two amplifiers - each for one leg/phase of the signal.  Speaker is connected between outputs of both amplifiers. 

Icepower 300AS1 module in S300 amplifier has balanced input stage and Mosfet bridge on the output (switching speaker direction), but is not "Fully Balanced", but rather amplifier with balanced input - often called "True Balanced" when done right (no GND reference)