Is there a strategy in preamp tube placement?

Hey @coachpoconnor, how are you liking the Linlai's?  I've been thinking about trying a pair also, but haven't pulled the trigger yet.   Also the Elite 6SN7 might be a little bit too tall for my setup, so I'm also considering the globe shaped ones available in Grand Fidelity, which are $400 a pair.   It's a lot of money to spend without hearing them first. Thanks.

I too have a Cary preamp that I bought earlier this year.  I got the SLP-05, and it has a pair of 6SN7 tubes for the balanced input buffer, and 2 pairs of 6SN7 for the left and right gain stage.  The stock EH tubes have good details in the treble and decent slam in the bass, but I found them to be a little too bright for my system.

So I bought 3 pairs of NOS RCA black plates to replace them all.  The RCA's are much warmer, less details but no harshness at all at the high end. The bass does get pretty low, but lack a little bit of slam.  Overall, I found them to be a little bit too dark.

So I changed the pair for the balanced buffer back to the stock EH tubes.  It sounded much better now with that setup (EH in the buffer, and RCA in the gain).  It restored some details on the high end, but without the brightness, and just a tad of improvement on the tightness of the bass.  So I kind of agree with @lewm that the tubes at the gain stage seem to have bigger impact on the SQ.

Anyway, I also recently bought some Ken Rad VT-231, based on all the praises I read here, and sure enough, they have very bad microphonic.   One minute into the first song I played with these KR, there was a sudden loud hum coming out of my speakers, and I ran to lower the volume down to zero, but the hum was still there.  I ended up having to power off the preamp to stop it.   I tried playing some songs again after a few minutes, and by chance I noticed a loud knocking sound coming out of the speaker when I just happened to tap the volume knob while trying to adjust the volume.  I then tried tapping the surface areas of my preamp, and every time it would be amplified and heard through my speakers.   I ended up returning them to the dealers and asked if he can find me some without the microphonic, but I haven't heard back.

Questions to you guys with the Ken Rad with microphonic.   How do you guys deal with this issue? or do you simply just live with it?   Thanks.

Thanks @lowrider57, I actually did purchase the Ken Rad from Brent Jessee.  Great guy to deal with.   My first set of RCA was purchased from him also.   I was going to hear from him if he's able to replace those KR that I sent back with something low noise and non-microphonic, but I haven't heard back yet.   He actually never mentioned any extra fee for noise and microphonic testing.   I wouldn't mind paying the extra if he can do that.

Anyway, reading some of the comments here, maybe I should just forget about the KR for my preamp.  The RCA black plates that I have are very robust.  No noise or microphonic, and sound pretty good.  Maybe I should just stick with those for now.  

Thanks @lowrider57 for the information on the fee.

I'm still fairly new in tube rolling, and learning a lot from this thread.  Thanks!