Was intrigued by this myself a while ago when I rewatched the film.
Checked this very useful site (it lists all the musicians taking part in the soundtrack:
http://www.filmscoremonthly.com/cds/detail.cfm/CDID/364/
Was delighted to find out Joe Mondragon was the bass player...
This should really be in the political section but it's also about music...
http://www.youtube.com/watch?feature=player_embedded&v=aUmubmoEjHo
http://www.wqxr.org/#!/blogs/wqxr-blog/2013/jun/16/video-greek-orchestra-tears-plays-its-last-concert/