changing buffer size in core audio using WL ?

I’m using Mac and Wavelab 8.5 with Avid HD I/O as soundcard/converters. I would like to change the buffer size from 256 to 512 or higher when mastering. Before launching WL I set 512 in the Core Audio manager. But when WL is lounched the buffer size goes back to 256 (like a default) in the Core manager and is stuck there, no alternatives avalible (greyed out).
Any advices on this are very appreciated!

Is this the digidesign/avid CoreAudio Manager? Does it save the new buffer setting if you close and reopen it, before opening Wavelab? Does it do the same thing when used with other programs, like iTunes or GarageBand? I guess you could also ask at Avid, but it might just require deleting the digidesign/avid coreaudiomanager .plist preference file, in home/library/preferences.

Or maybe it’s something like this:

and you can only set the buffer in Wavelab.