FUD reports RS780D, the AMD 790GX supports a new hybrid corssfire, can CF with IGP and two graphics card, here is their report：

“AMD’s upcoming RS780D or 790GX chipset will add support for a new type of hybrid CrossFire, as not only will the onboard graphics work in conjunction with a graphics card, but it will work with a pair of graphics cards for some very interesting CrossFireX setups.

We’re not sure how much of a performance boost you’d get from a setup like this, but an extra boost for free is never wrong. Well, free is a relative term here, as we’re not sure how many people would consider this platform when it launches, as starting out with integrated graphics and then moving up to one and then two graphics cards seems like an odd concept.”

It sounds interesting, but after few seconds i think this the “hybrid crossfireX” have some limitations. According to Game.amd.com, CrossFire section, the Combination Options Chart, you can see Crossfire is just like SLI, can not combine two totally different GPU by the internal interconnect. The hybrid CrossFireX of 780G can only support HD3450, HD3470, and HD 2400Pro/XT. According to our review, HD 3450/HD 3470 is a 55nm version of HD 2400Pro/XT.

So, my speculation is, the RS780D, or the 790GX can support hybird crossfireX, but it will be limit to what the GPU core the mobo use. If it use a RV635, then users only can Tri-CrossfireX with two other HD 3650/HD 3670.

All these speculations are based on this Combination Chart: