MB for AMD Phenom II x4 940 Black Edition

STOP. You have problems. You cannot use DDR3 memory with that processor.
The processor is socket AM2+, it can only operate on a socket AM2+ motherboard, and it can only operate with DDR2 memory. Have you bought these items yet?
What you need is an AM3 cpu, and an AM3 socket motherboard to work with the DDR3 memory you have listed above.
Or, you can change back to DDR2 memory. If it were me though, I would go with more modern AM3 parts, and the DDR3 memory.

Well, it's good you don't want to crossfire because that PSU probably couldn't take it. Rosewill PSUs aren't that great and I wouldn't really want to trust my system to one. The Phenom II 940 BE does not support DDR3 memory, only DDR2. If you already bought these parts return the memory and go with this instead

Mushkin Enhanced Blackline 4GB DDR2 1066
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

As for the motherboard

ASRock A785GXH/128M
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

Gotta go with megamanx00 on the PSU as well, Rosewill PSU's do not have good reputations with the enthusiast crowd. Hopefully you have not bought, or if you have already bought this stuff, you can return some items.
You really need to rethink your whole plan to get parts that work will work together, and do what you need at the right price.