Don to the best of my knowledge, the difference between SE and balanced is slight if any at all.
Depending on how the circuit is designed and the rest of the amp is...a balanced output could be "quieter" due to the
wasy the grounds are laid out.
Thats it in a nutschell AFAIK.
That said, I have both balanced and unbalanced here and can not tell any difference at all.
There also is the "advantage" of more power in a balanced setting....which could help if your headphones need it?