I have tried several different things over the years.
Everything from sending the bundles to individual tracks and more.
If you are working on a project together, the most efficient way I have found to work across the net is for you to record as much as you can to give the idea of the song.... export the wave and convert it to an MP3 and email it to him. I suggest leaving 2 empty measures in the song and be sure the click is audible in those 2 lead in measures.
When he gets it he simply sets the project up, sets the tempo and imports the MP3 and goes to work. Some folks don't like working with mp3, although I have never had issues with them.....waves are just as good and with a file server site, easy to share. He sends waves back to you since you are mixing the project. I use Drop box and simply share that folder with everyone in the collab. They are able to go in and get files and leave files.
Midi files for entire midi projects are small and are no problem to send in most cases attached to an email.
I just had someone send me a zipped project with 8 audio tracks in it. Sendspace was the file server.... aside from the fact that it's pretty hard to tell where to clikc on sendspace these days... all the links have some sort of DL on them and you don't want the crapware..... but I did eventually find the right one. A few minutes to DL it, and unzip it and it loaded up and ran just fine.
On the song Come & Go on my music page.... the music was recorded here with Sonar, while the vocals were recorded at another studio in the next town over, running Pro Tools.... we had absolutely no problems sharing files to make that song work.