Four headed accelerated desktop


I currently own an NVS 440 graphics card and four monitors.
I can enable one desktop spanning all four monitors using Xinerama, but this way the Xcomposite does not work. If I enable TwinView, Xcomposite is working fine, but the desktop is limited to two monitors.

Is it possible to have one desktop, spanning all four monitors, and having Xcomposite enabled at the same time with NVS 440 ?

What are my options? (buying NVS 510 IS an option, if Xcomposite can run on one desktop, spanning all four monitors)