Just to be clear in the post below, what I ultimately wanted to do with all four subs was have the following happen:
1) Left Watchdog get all the 30-80Hz of all left channel signals, mains/surrounds/subwoofer
2) Right Watchdog get same, for all the right channel signals
3) XS to get mono 20-30Hz
4) TRW to get mono 0-20Hz
Unfortunately, the Lake, although extremely capable, did not allow us to set a given output to be any mixture of inputs. You can have any output assigned any filter, but they all share the same input mix. Which meant for my application that I had to go mono to all the four subs above.