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If the modding doesn't work out for you, take another look at the PC-Q08. Plenty of room for an ATX power supply. I was using a 700w modular from OCZ in mine. Way too much power for an ITX system, and it's snug, bit it does fit.
650w is way more power than you need. The SF45ST is a great choice for a mini-ITX system. It's smaller than an ATX so it frees up room in the case and its got plenty of power.
http://www.newegg.com/Product/Product.aspx?Item=N82E16817256063&Tpk=st45sf
You have many choices for motherboards...
It's not unheard of for the SG cases to have noisy PSU's, which I always found odd. They usually build solid products. But if you don't want to RMA the case, you'll have to swap out the PSU. I don't recommend taking it apart and trying to fix it.
There's a guy here "Gaming twins..." that's working on a pair of systems with almost the exact same specs that you are using. He's got a pretty good handle on ITX builds and might have some tips for you.
I've just ordered the ASRock A75M-ITX and an A8-3850. It shipped today. I expect the have it in hand by Friday and a pretty good idea if a super-compact gaming system is possible by Sunday :)