Noticed a subtext in the BM preferences in SYS PREFS that states:
"Final Cut Pro X and startup video output will use this setting"
Seems like FCP X does not see anything beyond what this is set to upon FCPX launch as an AV option. Annoyingly, it seems to only be able to set this upon startup of FCP X. So I can't change AV output on a per "project" basis while FCPX is open... ?