Yes. Sell the 7800 hub and buy a 6600 or 7850 hub.
Sorry, couldn't help myself.
The only possible fix is if a 7850 cassette body will fit on a 7800 hub. It may.....or may not.
(will not be cheap)
That 7800 hub is 10 speed specific always. The 7850 hub came out because enough people complained that they couldn't put their old cassettes on the new hub. It's kinda' like when campy came out with their Aluminum cassette body. People complained that they couldn't put their 8 speed cassettes on it. Campy told them......"Bite me".
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