Having the same issue here, low volume with 7218 asus driver. I reverted to 7023 too...
I've tested also all the new realtek drivers (provided by realtek), and the low volume is still there even in the newest 7283 (found here
http://www.station-drivers.com/index.php/downloads/func-startdown/783/)
I'm afraid 7023 will be the latest usable driver from asus, unless someone says that the low volume in newest drivers is intended and not a bug that affects quality.
A clarification from asus support will be much appreciated: we will be forced to stay with old drivers because all the new realtek ones are too quiet?
Is this bug experienced by other realtek chipsets, or supremefx only?