Are you sure you've checked the right MB? The official website says that MB is crossfire compatible, so my main question is still ON. If i take two radeon r9 graphics cards one 280 3gb and one 280x 3 gb are they compatible to crossfire?
Multi-GPU: AMD CrossFire Support
(MSI motherboards feature one or more PCI Express 3.0 slots, perfectly aligned and with enough space for an optimal airflow when using multiple graphics cards. That way, you will never have to worry about an overheating PC, while you are enjoying the best graphics jumping off from your monitor when running a AMD CrossFire™ gaming setup.)
Tom's Hardware article will most likely answer all your questions: AMD Radeon R9 2XX Crossfire facts and compatibility thread (sublink) - [Solved] - Graphics Cards
Copied from link above:
(Recommended Crossfire Setups)
R9 280+R9 280X 2/3/4 way (Bridge required)
All Possible Configurations: 280+280X / 280+280+280X / 280+280X+280X / 280+280+280+280X / 280+280+280X+280X / 280+280X+280X+280X
1) Motherboard -
-Does your motherboard support Crossfire and does it support it in at least X8/X8 configuration? It is not worth buying another card if it is to be bottlenecked in X4 mode. If you are needing to get a second card but your motherboard only supports X16/X4, upgrade your motherboard. *CPU PCI-E lanes are a factor with multiple graphics card configurations on motherboards.*
-If going over two cards make sure that your motherboard has the right slot layout. If planning on just buying two cards, check if your card is abnormally high and hangs noticeably over two slots *This is only an issue with cards are a hairline apart due to slot layout*. To check out your or another specific card specifications and size, go to the previous page, select the series and scroll down until the card your interested in is listed. If you have a large air cooler and it's extremely close to the first slot, DONT use it. This can cause a short circuit in your system.
-Make sure you have enough slots on your motherboard depending on how many cards your planning on buying.
If you find a motherboard that support Crossfire at PCIe x 16 at x8 speeds according to this website :PSU REQUIREMENTS - RealHardTechX
Two R9 280X Crossfired requires a minimum PSU Wattage for Total System Power of 900 Watts.
Two R9 280 Crossfired requires a minimum PSU Wattage for Total System Power of 800 Watts.
I really apreciate all your help. Thank you very much!