Edited by DeMoN1123 - 3/24/16 at 12:07pm
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.