I hope the seller on a 2nd hand site will contact me soon - I guess he should know. Problem is, Matrox often sells optional cables for special hookups, and such cables are often no longer available. So I hope to locate a 2nd hand "out-of-the-box" solution.
BTW, I am currently using a Matrox G550 with 2 flatscreens.
You probably already know this: the matrox parhelia 128mb comes with 2 DVI connectors, and one adapter that goes from one DVI to 2 analog (HD-15) plus one DVI-HD-15 adapter. Then there is also a tv output adapter that goes from one of the HD-15's to a split, S-Video plus composite video. So the card new has three adapters that comes with it; the tv output adapter presumably does what you want, just have never tried it myself.