Tubes for cary preamp Phono Section?

Hi everyone I have recently purchased a New Rega RP8 turntable with a Ortofon Bronze cartridge and i am running it through my cary SLP-98P preamp and Cary Cad120s power amp with great results. Now I had a person suggest.  That I can change the 12AX7 tubes from the stock ones to a different type to get more gain in the phono section of the amp. Has anyone tried this and if so which tubes did you use and any recommendation on brand? Also what where the results?