Using RemoteFX with older CPU series like Core 2 Duo / Core 2 Quad will not be possible, due to the fact of missing SLAT technology inside Core 2 processors. For use of RemoteFX SLAT is required and available since Nehalem.
Amongst others these cpu´s are not compatible with RemoteFX:
Intel Core 2 Quad Q6600, Q6700, QX6800, Q8200, Q9300
Intel Core 2 Duo E6600, E6700, E7600, E6750, E6850, E8200, E8300, E8400, E8500, E8600