Maximum content resolution is somewhat dependant on which generation of computer hardware is in the fixture, but as a general rule content should be around 750,000 pixels. This is calculated by multiplying the height x width of the content (for example 1024 x 768 = 786,432 pixels).
As an additional note, I believe the maximum size is 2048x2048. You will need to be running newer server hardware for this to work well, and even then only on a few layers (as opposed to all 9).
Also, the DL system is capable of projecting larger pixel count imagery using multiple units and Segmented Collage (up to 13,729x5,213 via 128 DLs in a 16x8 grid).
