Differential, Single-Ended, Balanced, Unbalanced, and all that jazz...

[somebodyelse]

Why do you say that? I don’t see why a simple RC filter could not achieve 12db cross slope without active components?

1] Transformer - unless it has a center tap to ground the hot and cold aren't ground referenced.
2] Passive/impedance balanced only drives the hot. The cold just has a matched impedance to ground, so only one of your RCAs would have a signal.

 

[HammerSandwich]

It will provide two signal of opposite polarity, yes, but I am not sure how or why you would use them to drive a SE amplifier (or pair of them).

Because you have an RCA-only power amp without a bridging switch?