Unbalaned to Balanced

How can someone say balanced doesn’t make a difference? Also, who cares if some amps only have rca connections? It’s irrelevant. If the equipment is truly balanced, use balanced. Balanced cables have better connectors, support much longer length, and is less noisy.

Getting back to the OP's question as I read it....
Unbalanced out to balanced in ( with an adapter) is quite simply unbalanced. Balanced lines have two cables, operating 180 degrees out of phase (push-pull) . The balanced input essentially measures the difference (sums them up). The big advantage is that any noise that is common - like noise picked up from RF interference or 60 Hz interference, ought to cancel.
If you run only one of them, its exactly like the unbalanced.

One caveat - this assumes that the amp’s in is true, inherently balanced meaning there is a differential input and you use either all or half of it. In this case you would incur no additional conversion circuitry. Sadly, more than half the unit I have seen actually convert balanced to unbalanced and then rn through the normal circuitry. In this case, unless you have a noise problem, balanced is inferior unless you actually like the distortion another stage gives (admittedly small if well done, but in theory, its there).

So bottom line - it should mostly sound like unbalanced since it IS unbalanced with minimal or no differences.
G

To your 2nd question, no specification will tell you.
And manufacturers don;t want to say " i have a single ended circuit and plopped an op-amp (or 3, to make a classic Instrument Amp Configuration) on it to convert it to balanced".  Or whatever.  But often it is true.

And again, aside from noise immunity (and 3dB more gain, but that's also mostly a noise benefit), there is NO DIFFERENCE between unbalanced and balanced.
On most of my designs the input is a differential amp anyway.  So they are the best candidates for balanced. And even with my stuff, the only difference i know of, or hear, is noise immunity; unless one runs the amps as fully balanced monoblocks, and that's an entirely different situation where you get more voltage (power) too.
Moral of the story: don't sweat it. If you have noise pickup, route the wires away from the noise.