Which FreeBSD version did you try? I'm just skimming things, but it looks like Adrian Chadd might have updated the relevant driver back in May/June, in time for FreeBSD 11.
If its for the broadcom cards that's probably still a negative. I was running 11-CURRENT up until the release freeze and it never started working. That being said, it wouldn't surprise me if Adrian has it working by now.
Adrian has done a lot of recent work on 11ac in -HEAD, but not anything on BRCM of late.