Try the following........
Press HOME on the tv's remote to call up the menu:
Navigate to settings:
Navigate to sound:
Change " Target Input" from "Common" to the input used for blu-ray ( HDMI 1 or whatever ):
Scroll down to " Volume Offset" , and increase from 0 to a plus figure ( say + 4 or whatever ):
Now the volume for that input should be increased , so you shouldn't have to crank the volume up as much to get adequate sound levels , while leaving the dynamics unchanged. Works for the w5500 model so should be the same for the z series!