What improvements would I get with a "better" preamp?

That's all good info about the Cary.  I have an older version with the large generic oil caps.  It's not BAD, but compared to the Aikido circuit, it's slow and thick-sounding.

@decooney I know that you have a lot of experience with these preamps and the tubes that they use. Mine has the Hexfreds and is direct coupled, which I"m told, increses the speed. I don't understand half of it, just know what I'm told and how I perceive the way it sounds to me. I think of it as sounding mostly very natural with great detail, excellent treble and mids and solid bass with good slam, all of which is completely dependent on a very good tube compliment. Without good tubes, a very solid piece of gear can sound pretty dismal. I think you would agree with that and is pretty much the point that I'm trying to make to the OP. 

Thanks! I'll seek out some better tubes, tho my main source,  Brent Jesse, is closing (has closed?), from what I've read somewhere. 

I can run 12SN7 with the flip of the switch. Any 12SN7 as good or better?

@rockadanny I don't know the 12SN7's as I can't use them but they are often cheaper since not many can use them. Ask Brent. He'll know what to do and will have something that matches well with your gear. 

March 2 was final day to order tubes from him. Super bummed.