I currently have a brand new CS-6600 Ultegra 11-23 10 speed cassette on Ritchey WCS Protocol wheels. I bought an SRAM 1070 11-28 10 speed cassette and took it to the LBS to install it. The LBS tried to install it and said they couldn't do it because my SRAM cassette was incompatible with the freehub. My documentation that came with the SRAM 1070 and everything else I've read states that it is compatible with all "shimano compatible driver body" EXCEPT Dura Ace. My cassette says CS-6600 right on it so it aint Dura Ace. Anyone else replace an Ultegra cassette with a SRAM 1070?