lightbox's right, every single physical output (bottom row) in TotalMix has it's separate mix, that's a sum of all the hardware inputs (mics, line ins.. the top row) and all the software outputs (middle row) that you want it to be. Nothing can directly send anything to any hardware output, it all goes through the sub-mixes.
This means that even if you have a ASIO software sending it's output to "Out 1/2" it doesn't actually go directly to the physical output 1/2, it goes to the middle row of faders to the channel "1/2". Then when you've set all our signal to the software outputs you want, THEN you create a mix to your desired physical output by clicking the hardware output channel on TotalMix to choose it, and then using the faders on the middle and top row to choose what signals you want to mix into that physical output. EACH output has it's separate mix.
It's really, really powerful. You just need to understand how it works.