I’m not sure I fully understand what the issue is.
AFAIK there should be no issue when using the latest RME drivers with Wavelab. If the RME clock source is set to Internal, the sample rate changes automatically according to the file you play in Wavelab. Playback of 44.1, 48 and 96kHz files normally functions flawlessly with a Wavelab / RME combination. (Once Wavelab is in control of the RME interface it is normal that the sample rate is greyed out).