I'n not quite certain what the problem is, but i am using an Asrock FM2A85X Exteme 6 mobo with a A8-5600 APU. On its own, most Blu Ray videos are quite choppy. With a radeon HD 6670 in what was formerly called 'crossfire x' video is perfect with the display either connected to the mobo vid port of to the card. I have tried multiple time with card in-card out and still get the same result.
"CrossfireX" actually refers to all Crossfire.
Hybrid CrossfireX was the former name for what is now called "Dual Graphics". However this mode is not necessary to play HD video like BD--the 6670 on its own will do that. UVD engines do not combine in CrossfireX of any sort (only one is used). The hybrid/dual part only helps for gaming, but due to FTV (Frame Time Variance) issues with Dual Graphics, this usually doesn't translate to any real-world performance benefit in games*. I.e. In reality it's better to just forget the Dual Graphics and run the 6670 solo.
*Though AMD has updated drivers to address FTV issues in standard CrossfireX (dual card) setups, I'm not sure they've done anything to fix the problems with Dual Graphics configurations.
That said, theoretically speaking you shouldn't even have needed to use a dGPU to "fix" HD playback issues. The A8 CPU you have does have UVD 3, and therefore
should be able to do HD video playback all on its own. Only things I can think about that would cause issues are older drivers perhaps or maybe RAM that's not fast enough. Otherwise I don't really get it--you certainly have an odd situation on your hands there. What
should be working either on the APU or the GPU alone, is clearly not.
As for the original question, for many users no add-in cards are needed at all with modern motherboards--hence the reason many HTPC users go with mATX and even mini ITX builds. If you can use/need tuner cards that'd be one exception. Also for gaming, a dGPU of course or even multiple for SLI/Crossfire. Other than that if you needed faster network and/or multi-network (teaming/aggregation) connection then I could see using a PCIe network card. Some people may also run RAID cards but I think that's more for server use than strict HTPC use.
Obviously it's totally situation/need dependent, but since so much has been built into mobos for the past decade or more, 7 slots a la full-ATX is just silly for a lot of people. Personally I haven't used a full size ATX board since the Pentium days--that many slots is
totally pointless for my needs. I've been at mATX and smaller since the PIII days. Today I have five operable non-portable (aka "desktop") PCs in my house and not one is full-sized ATX. Over the years mATX and ITX boards have become more common and have a lot better features and functionality as they once did (particularly in the OCing dept) which is good for folks that just have no use for the extra slots. If you do need the slots then of course by all means, otherwise I don't see what's the point in having an ATX sized build/board with 5-6 of the slots just sitting there empty.
