Unfortunately B5 version of FDE is not the same tone as magpul it is brighter. Learned it the hard way but OP is good about exchanges so no harm done. I went with Coyote on this build which is darker that Magpul FDE but not a deal breaker. IMHO
The B5 Systems Enhanced SOPMOD Stock offers a coyote brown option which would be the closest color B5 Systems offers to Geissele DDC.
yes, from what I can tell. The manufacturer's part number on optics planet matches the manufacturer's part number on the b5 website that describes it as the enhanced version.
The B5 Systems Sopmod Stock will fit on a Magpul buffer tube and anything else Mil-Spec.
No, this item does not include the receiver extension.
It should be close, but it is not going to match. There are almost no two manufacturers that make exactly the same color parts, whether that be by choice, or because of product material and other variables that can change the color of the completed product.
None of these color options will be very close, the coyote brown would likely be as close as you can get.