I usually run two instances of Live ("Live" and Live "Copy") and route them through Soundflower, respectively to channels 1-2 and 3-4.
Then I have a little mixer patch (see attachment) which allows me to mix between the two sources. And this works fine. The only uncomfortable thing is that I need each time to switch between windows to open the next live set, and it may take some time and create confusion.
I was looking to a solution like yours, so I can open live sets from the Max interface, I think I’ll just need to implement it in a Max abstraction and it should work, what do you think?