Tube pre-amp upgrade from Mcintosh C2300


If I want to upgrade my Mac C2300 tube pre, should I just move up within Mac line to Mac C500T or try an audio research Ref 5 or a Shindo Monbrison? Has anyone compared those?

My source is Linn Akurate DS player, amps are Mac MC402 and MC275, speaker is Wilson audio Sophia 2 with transparent Ultra cables.
yxlei
I personnaly have a LS26 pre amp with a MC402 and it sounds very good. However I have been wanting to upgrade as well and I really am leaning toward the C500T. I was looking at maybe a Audio Research LS27 or even the Ref 5 now that there are some used poppong up here on AG. But I am a die hard Mcintosh guy and really want to try the C500T. I haven't read any reviews on it, but the C1000 gets pretty good press. How have you liked your C2300? I had considered that when I bought the LS26 but at the time really wanted to try something different.
I have a Ref 3, and have heard the Ref 5 and LS27. I did not hear enough difference from my Ref 3 with either, especially the LS27, to motivate me to upgrade. I have owned the Aurieges, heard the Monbrison, and own a Masseto. If you do not need balanced or remote capabilities, the Monbrison is a far more musical preamp than the Ref 5 or LS27. All IMHO, of course. And the Monbrison includes a superb phono stage.
Have you tried any tube upgrades in the C2300? I have a friend that has a MC402 with a C2200, and he did some tube upgrades with very good results.