When I'm trying to listen closely to something in order to make judgments on the overall color and spectral balance in particular, I always look away from the screen and even close my eyes a lot of the time, because the unnecessary visual stimuli of the waveform, or the cursor, or whatever else, has a very definite negative impact on my ability to make good decisions. That said, despite the fact that visual stimuli does play a role in mixing audio, I think your statement is still 100% correct, as the McGurk effect seems to only describe the interaction between hearing and vision specifically in speech perception, not any or all audio in general.