I would not recommend doing so as the performance increase will not be satisfactory. i suggest you guys just buy a discrete graphics card like amd radeon 7750 or 7770 or 7850 depending on your budget and disable the onboard graphics altogether. this would give you much more performance than what the crossfire would give you and crossfire is not supported by many games either so its best to just get a separate graphics card like 7750.
I use a 7850 clocked to 975Mhz with my A10-5800K playing games like BioShock, TombRaider and a slew of NFS series games. Olders games like Halo, Doom 3 rock too.
AMD A10-5800K, XFX 7850 Ultra OC Edition 975MHz, 16GB RAM, Win 8.1 Pro 64 bit, MSI 7778 motherboard, 500W PSU, HP P7-1235, CCC 13.12 WHQL