There is a link setting to control multitrack audio. But if linked as stereo modify clip multichannel audio should let you unclick the green stereo option.

I'd add that I'd remove the corrupted, no longer needed media first. So you clips show as offline before relinking. That way you can be sure the clips are linking to new media not the old media.

AAF is an Avid created protocl but its not well supported by other NLEs so using it to move outside the AVid world isn't easy or ideal. Its not a reccomended workflow at all. You should get a sequence as thats what an AAF is and normally Premiere does show a sequence but you wont have media connected to it (and will struggle to achieve that) Plenty

Also how much RAM have you got? How is you storage connected? Is it USB3 or Thunderbolt? Is it a Raid or SSD?

The media that comes back from Resolve has the baked in grades inside them. The MXF media is the graded media. Having access to the camera sources is important if it Raw media like Red. And to get the most from the grade you really don't want to be working on a Transcoded copy of your sources.

Also remember if you want to create the return Avid AAF in Resolve the original imported AAF from Avid has to still exist in the same location it was when imported. Resolve re uses that AAF to generate the return one.

I'm no fan of using mixdown I have that way. It locks you out of accessing the camera originals. You also can't grade the elements of an effect separately. My prefered workflow is to supply a guide of my effects. Sent to Resolve as AAF. Resolve ignores the effects it can't cope with but I can grade the elements. Then send the AAF back to

Try AMA linking the exported file back into Avid. See how it plays in there. When you say high pitched what foes that mean? Does it sound faster so the frequencies are higher? Or is it tinny (high frequencies loud low frequencies quiet) Are you sure in Avid you have the panning correct and don't have doubled up mono tracks that are cancelling out

I'd always keep framerates ti the final online where I can decide the best conversion.

There are common code elements shared by both PT and MC. If the versions aren't compatible installing one can break the other. It's that simple. If you need both installed you need to ensure you have both apps at the correct version (and that's not often the most current version)