One thing about adding a drum or other instrument to a mix after the fact..... the new track will not be treated with the same FX that are in the master bus.
Trying to get it to set properly and sound like it's part of the original can be done, but it's a bit tricky at times. I've spent more than a few hours to try that very thing....
I tend to put music I write and work on (for others) on my MP3 player and listen to them during the day as I drive from one job to the next. There are a few nits I have heard that I might would have done a bit differently.
As it stands, I pretty much worked on this as Mike sent it. The changes are:
I replaced Mike's drums with Jamstix and he in turn replaced that with his again. I sent 2 mixes.... one with JS and one with no drums.
I added the harmony electrics. They are panned out a bit... not centered.
I added one high harmony track vocally.
Everything else was Mike and his musical tracks.... I did "fix" to a lesser degree, his lead vocal track using melodyne to tweeze a few places but I wanted to leave some of the character in his vocal performance.
The tracks original FX were all removed and I started with the stuff I use..... since Mike & I have different plugs, that was the only option. Most of this is cake default reverb and EQ. I did use Ozone 4 in the master and possibly on the vocal bus...I'd have to look in the project to be 100% sure.
Anyway, we had fun working on this....