as i can have both the Xonar DG and onboard Realtek ALC892 installed at the same time
Not a good idea - Dedicated and onboard both enabled.
Try ;
Driver sweeper in Safe mode - Removing anything audio related
Shut down.
Boot into Bios - Disable onboard.
Restart Windows in Safe Mode - Install Asus drivers.
Reboot Windows in Normal mode.
Had to do it today to get my Essence STX to install properly, after driver hangs in normal mode.