Hi Timrhu,
Thanks for your comments - I'd say the Obelisks has a more solid soundstage and placement of the performers, instrumets etc. are that much more solid than the Arcs - see my review over at www.audioreview.com for more info.
However, I would say the Arcs are easier to live and get a beter result with if you have a small room and have a greater power handling capability than the Obelisks (200watts for Obelisk and 250 for the Arcs) which may also be a consideration if you have a powerful amp. I dont think you'd need an additional subwoofer as both the Obelisk and Arc go pretty low.
Hope that helps.

