The Silver Order (Harbinger) downed the first 2 bosses as a group this am, then we teamed up with The Order of the Seekers guild and took out Xeno II on SM & HM. With enough HP and good healers all but Xeno 2 Hard can be solo-tanked.
Xenoanalyst II Story: http://img809.imageshack.us/img809/2...3021214492.jpg
Xenoanalyst II Hard: http://img802.imageshack.us/img802/7...3021216313.jpg
Xeno 2 Hard Mode drops Rep and Helix, I think in story he drops less of them. Don't recall though.