Xonar DG(front panel) ---> Headphone
Xonar DG (optical out) ---> DAC ---> Amp ---> Headphone
Xonar DG (RCA Out) ---> Logitech 5.1 X-540 Speakers
are there any problem for my setup??
No problems with your setup.
The Xonar DG "might" be able to output (PCM) Dolby Headphone surround sound thru the optical output (maybe).
I know the some of the more expensive Xonars can.