Tube rolling 12AX7As

I'll echo Wolf_garcia in recommending the Psvanes. When I owned the C2300 they were my favorite, and I rolled in plenty of NOS and new production 12AX7. RCA black long-plates from the '50s were also nice in that pre-amp, but they're a bit pricier and harder to source.

I, too, use the Psvanes in my C2300. Grant Fidleity is the outfit I would purchase them from. Get the higher grade tubes.

Look at the block diagram:
http://www.mcintoshlabs.com/McintoshDocumentMaster/us/c2300om04.pdf

First off, there is a difference between 12ax7 and 12ax7A
"The published difference is that the 12AX7A can be used with heater circuits wired in parallel and series, whereas the 12AX7 can only be used in parallel circuits."

So you need to determine how the heater circuits have been wired before you start. How to tell??? Pull one tube briefly and see if they all go out. Just like Christmas Tree lights. One bulb blows in a series connection they all go out. One bulb blows in a parallel connection, the rest stay on.

If you pull one tube and the rest stay lit, it's wired parallel and you can use either 12ax7 or 12ax7a
If you pull one tube and they all go out, it's series wired and you must us 12ax7a.

The first two tubes do MM phono
The next two tubes do MC phono
The last two tubes do the whole preamp.

The phono tubes (one thru four) should be low noise tubes like 7025 or 7025a
The last two tubes will determine the final character of the sound. Personally, I like NOS Amperex. Tele's are strong but sometimes overbearing. NOS Mullards are also nice, maybe a bit heavy on the bottom end compared to Amperex.
Anything old RCA is great, as are Sylvania's in my opinion.

Roll away, that's the fun of it! It's like changing the strings on a guitar, they all have their own signature sound.

I too like the JJ 803S having tried all the current 12AX7 and several NOS versions; nicely detailed with great staging and warmth. Not etched or strident at all, great textured bass too. Preferred over current Genalex version IMHO.