My "native" platform is the Mac and so I too find some aspects of VS a bit bewildering. I have also experienced that it is sometimes more predictable to edit the files in a text editor.
Making a sln from a bunch of vcxproj files is pretty easy probably it won’t have to be updated at all (you probably just need to update the vcxproj files). I say "probably" because its impossible say universally that it will be okay.
As of the Max 6.1 SDK we are using props files for our projects. Perhaps this will help in figuring out how to update your vcxproj files because ours already have similar references in them.
Unfortunately, I can’t provide a silver bullet, but hopefully it won’t be as painful as creating those files in the first place!