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?
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A 12AX7 is the highest gain tube you can get in the 12 type tubes. All others 12AT7,12AU7,etc. are lower. Here is a chart for the gain! It should help!

Yogiboy is right the highest gain of the 12**7 family is the 12AX7. And they all sound different. My preference is for NOS ones. To give you an idea of my experience of just some of the sound types.
 Seimans, Telefunken for analytical monitor type sound.
 Mullard Brimar soft'ish big robust type sound.
 RCA, GE in-between the above two.

My favorites were nearly always RCA, in all the families of tubes, especially black plate versions of the massive 805 DHT transmission tube.

Cheers George  
As Yogi and George have already stated, you will not get any more gain from another 12Axx tube type.  The circuit was designed around a 12AX7, so you're best to stay with that tube.  You can likely improve the sound quality though with a different tube, especially if you have the factory supplied EH or run-of-the-mill Chinese tubes in there now.  I (personally) do not like Mullards in anything made by Cary...too soft, veiled, and sluggish.  The RCA's George mentions are a really good prospect, but a genuine NOS pair will set you back some money.  The new-manufacture Gold Lions are very good, not to the level of a black plate RCA, but much better than the factory tubes and won't cost you an arm and a leg. In any event, if you decide to try different tubes, I would highly recommend you buy replacements from a trustworthy, established tube vendor that carefully screens and tests the tubes for noise, as that will be a critical parameter for the phono gain application.
After using various NOS 12AX7s and other new stuff as the drivers in my tube amp, I bought a matched pair of the new Gold Lions and they're very good…stable, gold pins, relatively inexpensive, excellent tonal characteristics or lack of same (which is a good thing).
When i bought the preamp I got some 12ax7 gold pin JJ teslas from the dealer and made a bit of a big difference from the Stock Chinese Tubes. Though i have never tried gold lion or how they compare to the Gold Lions? What are your guys thoughts are the Gold Lions a bigger upgrade from the JJ's? and would like the next step up from them.