So the 8 speed cassette didn't rub, the 10 speed cassette didn't rub, but the 9 speed does? I mean that does make sense because the 9 speed cassette is ~1mm wider than than the 8 speed, and the 10 speed Shimano cassette is actually narrower than the 9 speed because the largest cog is dished in. Seems like the best course of action would be to run a 10 speed cassette. Didn't you say you already have the SL7900 shifters?
edit: Hold on one second! You said Miche 9 speed cassette- Are you using a Miche cassette that is meant for adapting a Shimano HG hub for use with Campagnolo drivetrains? These are wider than the Shimano 9 speed cassettes. See the Sheldon Brown cog spacing crib sheet. You need a Shimano/SRAM 9 speed cassette.
Last edited by icemilkcoffee; 09-19-22 at 11:33 AM.