I only listen to the core layer, and haven't noticed any unusual audio problems. Using a 100, 200, 436 and 536. The 200 and 536 are on different antennas. Of course, the OKC system has wild volume fluctuations, audio overload at the transmitting end (especially the FD), sometimes the person talking sounds like they are right in the room with you, and sometimes they sound miles away. Sometimes on my 436 it sounds like the speaker is blown, but it's just their audio. I don't have any of these issues on OKWIN, except for the awful analog simulcast distortion, which neither the 100 or 200 can fix.
Wouldn't you be missing Transmissions if you only listen to core layer