There are a lot of great ways to collaborate on tracks using Splice.
In addition to sharing project files and folders you can also share audio stems within DAWs among users.
If you find the first one, Logic will find the rest.
NOTE: We found that the AAF format maintained region names and track names, OMF did not.
This is the fundamental point of most people's frustration and trouble with OMF and AAF files.
As a professional mixing engineer myself, these are the things that I consider outside the range of normal mixing duties, and that I will charge extra for if they weren’t done before the files are sent to me.
The real downfall is the inability to maintain track playlists, but we've all learned to take whatever we can get I suppose.
One needs to include notes when sending AAF files to another person as to the sample rate, bit depth, and frame rate of the export as these things aren't inherently imported.
Once you have decided that it may not be best to try to do it all yourself, and you think you have a song that is good enough to get professionally mixed, you need to prepare your tracks to send to the mixing engineer.
Most professional mixing engineers will be happy to tell you what formats they accept and how to get your tracks into the proper format to deliver to them.