You don't need to do the actual mixing in the software necessarily.
I record by channel and further process the mix. I want to deliver a good mixing and that is impossible just by recording a straight output from a shitboy. I do make it as good as possible in the machine beforehand, though.
Now mastering is a bit of a different science altogether and I only leave it to experienced sound engineers after I gave them what I think is the best mix I can output.
In a lot of cases people confuse mixing and mastering, to me a mastering process is done when the final mix is done and you need to deploy to a lot of different media and it needs to sound the best in them all (digital download, Cd, home computer use, big stereo, etc). This is way over my head.
If I am not wrong Glomag is a sound engineer and he probably mastered the files IAYD gave him. For mastering, you only need a final bounce of the file to be mastered, not a channel-separated package. Then they apply their secret magic science.