Hi Nicola,
I have tested both outputs in the same rig (the input gain on the single-ended pre-amp input was a little more than 6 dB if I recall). Subjectively speaking, most of the time the louder sounding source will seem to be better - which is not necessarily objectively true

. After testing I am now using XLR, but I would not say the difference was dramatic. If your player will be seated close to the amp then I think you should not bother too much, as balanced interconnects tend to show their advantages over longer cable runs.
Curious how the G08 will sound paired with the Bryston.
Cheers,
Dorian