I need some information regarding a multimonitor setup:
I am using a R600 card with DVI/VGA/HDMI port with mesa(gallium)/drivers from git and want to know if it is possible to use two monitors at the same time with this hardware/driver combination (monitor 1 using DVI and monitor 2 using HDMI). If not, how well does a multicard setup work and do I need two identical cards for that or would e.g. a R300 card do the job too?
All Radeon chips support multi-monitor on Linux, with the open-source driver. Your card only needs to have 2 or more connections. All types of connections - VGA, DVI, DisplayPort, TV-out, HDMI - are supported. And on the R600/700, also the HDMI audio works.
Multi-monitor should just work on your setup. You may have to configure the 2nd screen in the display preferences if you don't like mirroring: the same content on both screens. But you can easily change this in the display preferences of Gnome or KDE.
Just connect your 2nd screen, wait 5 seconds and it works. Multicard should also work, I've never tried it so can't tell you more about it.