Biostar is generally a decent product, with occassional complaints on quality, but usually from the enthusiast crowd. With your type of low demand usage, it should be fine, but an upgrade to a better brand (Asus, Gigabyte, MSI for example) might be up your alley, for a few bucks more and perhaps a bit more peace of mind.
Here is the 890FX search page from Newegg.com, as long as the Mobo has 4 x PCI-E x16 slots (even if they only run at 4x, would suit your needs, x16 is more for gamers) If you can get away with only needing 2 slots for 2 cards, then there are even cheaper options that will do what you need. For example, a Gigabyte 785g 2x PCI-E slots x16/x4, for example, would be less half the price, but still a solid reliable product than can run 2 cards in the formation you are persuing.
Your requirements wouldn't stress out the CPU enough to cause heat issues. Assuming you keep it clean, even with the stock cooler it will be a cool running quadcore, and its only 95w. There was a 65w Phenom II quadcore (910e) but couldn't find it on the egg, and it would probably perform lower, and cost much more than the athlon without a huge edge in power consumption or heat production.
Hell, you might even be able to get away with using a 65w dual core Athlon II, but there may not be as snappy and impressive as a quad when you have all those screens running.