I currently mix in Logic and had a small, custom made passive analogue summing mixer built a couple of months ago.  I come out of the back of my Focusrite Saffire Pro 40 
Kick - out 3
Bass - out 4
Perc - 5+6
Guitars - 7+8
Synths and Fx - 9+10
Then record this final summed mix back into Logic...