I listened to the conference call, and everything I've seen, outside of CB, has said they stopped just short of voting for expansion. When I listened to the call I didn't hear them say they voted unanimously to expand. The transcript of the call doesn't say that either, just that they voted unanimously to explore it and contact interested schools.
http://www.big12sports.com/fls/10410/pdfs/quotes/transcripts/071916BowlsbyBoren.pdf?DB_OEM_ID=10410
Did Boren say something in a follow up interview or something? - Not trying to argue here, I think it is clear they will expand and the only real questions are who and how many, but I just haven't seen something from the Big XII that states as unambiguously as you imply that they voted unanimously to expand as opposed to merely contacting schools and exploring expansion. Do you have a link?