In agreement with Richard...
The graphics suck.
There is no graphics memory. The GPU is very small and very basic. It uses system memory and gains this system memory at the expense of the CPU performance. The CPU is also busy accessing the SATA controller so you'll also downgrade your playback performance.
Triple head is a very very bad idea on a Mac Mini. Single output only 1920x1080 or smaller.
It is possible to crash Catalyst on a Mac Mini by overloading the video card with very high pixel resolution such as a TH2G. They system tries to buffer too much memory to a paging file and the system will lock.
This is rare but it has happened to me. (granted I obscenely overload things to test them)