Instead of a splitter, I setup Fuzzmeasure to output on a Soundflower audio bus, and then used Audio Hijack Pro to route the L channel of that bus to both the L & R speakers coming out of the motu. Saved $2 and a trip to the Radio shack
Attached is the 'final' graph from 20hz-10kHz in my room after everything is moved in. Still not really pleased with my uber small sweet spot, but for the size of the room (and without covering the window) I think it's close to the best I'm going to get.
I don't mind the 'deadness' in here... I might try the cardboard trick, but it seems like to much of a pain right now!!