I've been using Live 8 with various generations of Motu 828s in several venues for quite a while, and I've never had this issue...
Usually, when I fire up Live and open a pre-made file (external outputs mapped etc), it opens with the motu 828 as it's output and the correct outputs enabled. (IOW - I don't have to go through and select "Motu 8282" from output instead of "Built-In Output" as long as the motu is powered on, connected, etc. AND even if the motu was powered off, then powered back on and selected, all of the correct outputs are still enabled)
On my latest ableton rack I used an 828mk3 hybrid, and every time I open live, it reverts to the "built in output" - then when I go in and select the "Motu 828mk3" I have to go and enable the correct outputs (only the default "1&2 stereo" or whatever is enabled) Any advice to getting this sorted out?