Just buy a single one with the i5-3570k, or a i5-3470 + 660 gtx ti/670 gtx/7970.
Oh and with two 660 gtx its called sli setup they're from nvidia not a crossfire setup(amd).
Two 560 ti sli will offer poor value for the money nowadays, the 660 ti gtx performs the same as that setup with less troubles and power consumption.