This is actually on OSX 10.13.6 but I expect it would be the same on PC & this will get a wider audience:-)
I only got an MP4 viewer of 1 camera & the seperate audio files when I started the edit. Typically I’d use PPro because I can edit multicam groups at any time to add additional cameras... but now I can do that in Avid so I thought I’d give it a go.
Yesterday I synced the MP4 & the audio files as a group clip & did a rough cut.
Today I got the full res 4x cameras so edited the group to replace the V1 and add 3 more cameras. I clicked ‘update’
Then right clicked rough cut & refreshed groups. All the waveforms redrew but the timeline video remained the MP4 clip & mulicam mode showed only 1 camera.
Match frame matched back to the correct, 4 cam, group so it was pretty easy to just replace all the edits I’d done.