I think they did a MF concert back in July, no? Been waiting to see Megumi and May'n perform Lion live together. Hopefully someone will find it and upload it soon as the concert DVD is released. I've searched youtube and niconicodouga already but no luck.
It wasn't really a Frontier Concert, it was a Yoko Kanno concert. I was there and it was mind-blowing.
May'n's performance of "Diamond Crevasse" was a total show-stopper. They extended it out to probably nine or ten minutes of slow-burning drama.
Megumi Nakajima also did a great version of "Voices," which I think is floating around on youtube.
As good as the Frontier stuff was, though, I was made happiest by the Cowboy Bebop songs.