That board probably has the original BIOS which didn't have support for the K-series 2600 at launch. If you update the Bios you should have it correctly listed. As for being able to overclock the processor with the multiplier; I'm not sure if that motherboard will allow it. Many of the intel boards don't allow any type of overclocking and I have seen a few that have had some ability. Intel's website doesn't show me much for that, so I don't know. However, upgrading that board isn't going to do a "lot" for performance as the only huge advantages of the Z77 boards is PCI Express 3.0. You have a Sandy bridge processor which eliminates that in the first place.http://processormatch.intel.com/CompDB/SearchResult.aspx?BoardName=DH67CL
If you're wanting to overclock though, I would highly suggest a nice Z77 board if you're buying a new one; but if you're not going to overclock and that motherboard doesn't allow you anyways; stick with it as it's a great stock clock board.