D-Tek Industries are currently offers a range of 4 units which sound like they may be suitable for your needs.

The D-Switch (4 Inputs 1 Output) and the D-Swith Pro (4 Inputs 4 Outputs) are DMX controlled video switchers/matrix units. These units allow the user to route switch video signals, but require genlocked video sources as the D-Switch series has no frame buffering built in.

The D-Mix (4 Inputs 1 Output) and the D-Mix Pro (4 Inputs 4 Outputs) are DMX controlled video mixing matrix units. These are fully frame buffering and will mix (dissolve) multiple video sources to an output(s).

To mix more than 4 sources or output more than 4 outputs, all these units can be used in combinations to provide a mixing/matrix solution.
Ie: 4x D-Switches running into a D-Mix Pro = 16 input, 4 output mixer.

The D-Switch and D-Mix series units are all currently Composite Video and S-Video units, so convertors or input/output cards will be required to run into or out of a catalyst, but there are a number out there.

More Specs on D-Tek units can be found at
http://www.d-tek-industries.com
or http://www.projectedimagedigital.com who are the distributors.

Hope this helps, any questions, please feel free to mail me at dan@d-tek-industries.com

Dan Cook