Please refer the ATI's list of VGA card model which can support Hybrid CrossfireX.
HD4350 is not the Hybrid CrossfireX supported model.
However, it will be able to support CrossfireX by using two HD4350 VGA cards.
http://game.amd.com/us-en/content/images/crossfirex/CF_combo_chart.jpg
Please refer our FAQ for motherboard and VGA card combination to support Hybrid CrossfireX.
https://www.biostar.com.tw/app/en-us/support/faq.php?S_ID=389
