AAF is a container, kind of, like OMF.
It can be embedded style, being content is embedded, or just reference external files.
If really big project so it pays off time used, you might use a converter like AAtranslator to convert to OMF.
http://www.aatranslator.com.au/ Otherwise better to just drag-n-drop audio files over to Sonar.
There is no standard, as I have found, to exchange midi files like this - so if many midi files, even less reason to use AAF/OMF.
With over 30 years of midi - strange that no exchange format popped up including midi parts.
Best result I had was moving projects from Reaper to Cubase, was over EDL format through Samplitude and then export to OMF.
Hope you get some ideas.....