[DeMoN1123]

del

 

[PurpleAngel]

If anything, you should be getting a very loud bass with the SB-Z and DT770 Pro 80-Ohm combo.
I've tried a few Beyers with the SB-z, did not have a volume issue.
 
Did you disable the motherboard's on-board audio? in the BIOS.
 
Might try doing a really fresh install.
Delete the Creative software
Then turn off computer and remove the SB-Z.
Boot computer to Windows and run the program ccleaners (both Cleaner and registry functions).
Turn computer off and install SB-Z
Turn on computer and install Creative software.

 

[DeMoN1123]

Thanks for the reply. Yes, I've disabled the on-board audio in BIOS. 
I'll try to reinstall the driver as you said. Thanks!