@Andykong As I was using the single ended connection for the Empyrean, and switching around various modes i.e. UL / TR, and impedance settings, when I'm on UL mode, and flicking the impedance switch to low, there's a moderate high pitched tone coming into the headphone, not loud but moderate tone.It probably is related to music genre as well. If you listen to a lot of vocal, with only one or two instruments in the background, single-ended connection will offer a more focused presentation, with the singer right in the middle of attention. If you listen to symphony, live jazz band, or more complicated music with multiple instruments, the strength of channel separation will come into play and the balanced connection will work better.
In addition, music that demands transient and control will be better off with balanced connection because of extra current, but if want to have an laid back and easy listening afternoon, use single-ended.
So balanced vs single-ended is more then higher output power. I think its worth getting both 6.35mm and XLR4 (or 4.4mm) cable when you acquire Empyrean.
Flicking the impedance to medium the tone stopped completely. Further experimenting, low impedance and TR mode is fine, as with other combinations. Just combination of UL and low impedance seem to have caused this issue. Is this something others experienced as well?
FYI the amp is on EL34 tubes with the switch at the back on EL34 settings as well. Not overly concerned but thought I check as it's interesting.