I have done this for several years on my home Ubuntu machine. (Dual monitors with HDMI out including audio).
Nvidia cards are much better supported than ATI, by both proprietary and open-source drivers. I use the proprietary ones. This is my current card, which works well: http://www.amazon.com/gp/aw/d/B0086UXQES/ref=redir_mdp_mobile?ref_=pe_175190_21431760_M3T1_ST1_dp_2
I use Cinnamon (from Linux Mint) as my window manager. Gnome Shell has a better handle on workspaces than Unity does in my opinion. Cinnamon is most configurable of those three wrt workspaces.