Just got a new power amp

kijanki

He talks about benefits of balanced cables and differential inputs. It has nothing to do with "Fully balanced power amplifier"

Actually, it has everything to do with "fully balanced" amplifiers, and @atmasphere  is especially well known for his balanced amps. Owner Ralph Karstens even holds an interesting patent covering his topology.

I've now provided to you three original sources that reveal your beliefs to be myths. 

kijanki

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

I understand that intuitively what you wrote seems "true," that it "feels" like it's correct. But it is completely false. You don’t know what you’re talking about. Here’s a guy who actually understands balanced circuits and who notes the myth of your claim. (I suspect you’ll reject this,  just as you have the information I’ve quoted from other manufacturers. I’m including it for the benefit of others):

Balanced line equipment is often also fully differential, like our amps and preamps. A differential amplifier has two inputs, and in theory only amplifies what is different between those two inputs ... A differential circuit isn’t double the number of parts of a single-ended circuit, although it does have more parts.

kijanki

"Fully Balanced Amplifier" term refers to amplifier consisting of balanced input followed by two separate amplifiers - each driving one terminal of the speaker.

Of course you are free to define terms for yourself anyway you like. But a "fully balanced amplifier" doesn’t require two separate amplifiers. You simply do not know what you’re talking about and your claim conflicts with the manufacturers' published literature.

An amplifier using balanced inputs, balanced circuits and providing balanced outputs is, by definition "fully balanced." It’s as simple as that.

kijanki

I don't see anything in specs showing fully balanced operation.  

Look here. Big clue:

Input impedance 

Unbalanced 50KΩ
Balanced 100KΩ

After balanced input, there is only one path (one amplifier).

So? You seem to not understand how a balanced amp works.

This amp looks like it's differentially balanced, a perfectly valid approach. This is taken from the data sheet you provided:

Input Stage
The balanced input section provides signal buffering and anti-aliasing filtering. The balanced configuration helps to avoid hum and noise pick- up from poorly shielded cables. An unbalanced input can be obtained by applying a short circuit
between Signal In- and Signal GND ...

Output Stage
The output stage is a full bridge topology with a 2nd order filter, thus the power output on the terminals Vo+ and Vo- is balanced ...
Warning: The balanced speaker outputs are both “hot”  (emphasis added)

kijanki

PS Audio S300 is not fully balanced ...

You might want to check the specs of the amplifier here. They certainly reflect those of a balanced amp.

Looking at the specs for your amp, I'd surmise you're going to have 6 dB higher gain on the balanced input. You might not need that gain, but you could also think of it as 6 dB better s/n ratio.

Using the balanced amplifier inputs also gives it a higher input impedance. That might be a friendlier load for your streamer.