For a general graphics workstation and expecially for 3D, I love dual socket boards. I've been buying them since before there were multi-core processsors. But for editing and DR specifically, I think single socket boards fitted with high (4Ghz and above) clock speed six core or better modern CPUs are probably better. This is expecially true if you intend to edit h.264 and similar media directly without creating intermediary files. However, things may be different for editing raw. I'm not sure how much processing is handled in GPU and if that varies depending on the raw format being used. If yer gonna edit raw, just ignore my post.
I think the key to happiness with DR is found in making sure you have enough GPU ram and speed and enough hard drive (think SSD or M.2 IMO) ram and speed for your intended use. So the right motherboard will be one that makes that easier by providing lots of 16x and 8x slots and flexibility in how the PCIe lanes can be allocated among the slots. BTW, with the current level of GPU performance, it is not yet important to make sure that GPU cards have access to 16 lanes in 16x slots. Current benchmarks with the fastest cards show that eight lanes works just as well. That's something to keep in mind when mulling over configuration options. In a few years, however, that may change.