conversion of single ended audio input to differential
It is possible that I have misunderstood the requirement - but if not...

The vintage way of getting differential audio signals from a single-ended input consisted of merely using an audio frequency transformer, usually a 2 pin input 3 pin output little thing, with a 1:1 turns ratio.

The single-ended signal feeds the transformer input, and the output side is a differential signal pair you can bias to wherever you need it to be - connect the middle pin of the output to ground, and the differential signal is ground-referenced. 

In addition, a turns ratio other than 1:1 allows impedance matching / voltage gain if desired.