EDIT: The Radeon HD 2100 IGP came on the motherboards with the 740G chipset.
Hybrid CrossfireX only works on the 760G, 780G/V, 785G, 790GX, 880G and 890GX chipset motherboards.
You cannot run Hybrid CrossfireX anyways, stick with the Radeon HD 6670 that you ALREADY have.
Why are you trying to run Hybrid Crossfire when your Radeon HD 6670 is going to be much faster anyways?
Doesn't seem logical to sell the card you already got, and buy a Hybrid Crossfire Compatible card, to get performance that's most likley less.
Not all motherboard support Hybrid CrossfireX, so please indicate which board you have. Additionally, for Hybrid CrossfireX only works with low-end Graphics Cards. Here are a few (older & newer) Combatibility Charts.
Chart 1: 880G and 890GX integrated chipset works with the HD 5450 / 5550 / 5570 / 5670. http://cdn.overclock.net/7/72/72ab03e2_AMD_CrossfireX_Chart_1618W.jpeg
Chart 2: 790GX, 780G, 780V, and 760G works with the HD 3450 and 3470. http://game.amd.com/us-en/content/images/crossfirex/CF_combo_chart.jpg
Your motherboard manufacturer's website / manual should have a list on what Graphics Cards (GPUs) are supported for Hybrid CrossfireX.
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