my question is: what kind of adapters should I buy?
I have searched around and there are lots of them, active, passive etc, and then there's the issue of the DVI, that in some cases you can use certain specific adapters because of it being analog (DVI A) or digital (DVI D) or both (DVI I)
I'm a bit confused on the subject, but I think that I have to buy a displayport to hdmi adapter and a dvi to hdmi adapter.
Will these 2 work with this card? : http://www.newegg.com/Video-Adapters/SubCategory/ID-304...
(any dvi to hdmi adapter) http://www.newegg.com/Product/Product.aspx?Item=N82E168...
that one or any other display port to hdmi adapter
To go from DVI to HDMI you can use an Adapter (the ones you showed would work fine) OR you can just buy a DVI to HDMI cable and skip the adapter.
For displayport, you want an active adapter. I would avoid the one you showed (only 1.1 compliant where as the card has displayport 1.2) and try one like this. http://www.newegg.com/Product/Product.aspx?Item=N82E168...
This one converts to DVI, so you'll then need another DVI to HDMI cable.
The same adapters will work with the second card you showed.
Passive is basically a port translator (fitting a square peg in a round hole). Active actually reconditions the signal. If you go passive you won't get the third monitor to work. It HAS to be active. Also, like AdioKIP suggested, even if you don't plan on using the added functions, it's best for compatibility sake to match all specs as closely as possible, otherwise you might run into other problems later on. There shouldn't be a whole lot of price difference.
Being an "Active" adapter was a lot more important in the past. When ATI first came out with EyeFinity (Being able to hook up and run 3 monitors or more as 1) you HAD to use a Displayport connection for one of the monitors and the adapter HAD to be an active adapter or it usually would just not work. As EyeFinity has evolved, it has become less picky about the adapters, but if you're buying one new why risk it? Better to just go with the ones you know will work which are labeled specifically as being EyeFinity compatible. The wholed displayport 1.1 vs 1.2 thing shouldnt matter, was just pointing it out.