The first clips from their last new XM show are up:
http://www.firesigntheatrelegacy.com/xmradio/index.html

Yes, the XM show is no more, as Ossman hinted at in the Fireblog
and Austin confirmed in the most recent Firesign Chat.  There
will be clips from show #11 and show #12 (which was made up of
clips from previous shows) up on the website over the next few
weeks.