CAT SL1 Signature, How does it measure up ?

Essrand, rolling in tubes is very easy in the CAT. Simply remove the top plate and you're good to go. HOWEVER, you MUST make sure that the new tubes that you employ are compatible. I have utilized Kevin Deal's assistance ( Upscale audio) with buying the NOS tubes. Kevin is well versed in what works in the CAT.
I cannot stress highly enough how large an improvement there is to be had over the stock tubes in the CAT.

I 2nd Daveyf - the CAT SL1 Signature Mk3 is a very good preamplifier. I used to own one for about 10 yrs - loved it each time I heard it. I "upgraded" to the latest CAT SL1 Renaissance recently. The Renaissance is better but not by a huge margin. The most improvement I've heard is in the upper freq range - the CAT SL1 Signature Mk3 was no slouch in the high frequency but the Renaissance gives the hi freq a little more air. You would never know unless you did a side-by-side comparison or owned one for a long time & then switched to the Renaissance.
make sure you get the SL1 Signature Mk3 which is the latest rev circa 1999. Yes, time has gone by but the fundamentals of this SL1 Signature Mk3 are still very solid & it's a great performing preamp.
I used NOS Telefunken 12AX7 for V8, V9 & factory tubes for the phono. the sound overall improved but it is very hard to find reasonably priced NOS Telefunken 12AX7 tubes!

you've never done tube-rolling. The act of rolling a tube is child's play. The real question re. tube rolling is how deep is your wallet? For some insane reason, NOS tubes today cost an arm & a leg....

Output impedance is a low 100Ohms so it should work just fine with the rest of your system.

After looking at the rest of your system, it's obvious even at first glance that buying the CAT would be like putting Michelin's best racing tires on a tricycle. Me, I'd get a Ducati Diavel before buying the world's best tires for it but hey, that's just me.

CAT"s owner Ken also suggested Mk III CAT Signature. However I can only find Mk II used, 2 here in audiogon now. Is there a big difference between Mk II or Mk III ? Definitely will tube roll.

I used to know what the diff between Sig Mk2 & Sig Mk3 but I have forgotten now! I would definitely listen to Ken Stevens - if he said he prefers that you get a Sig Mk3, then, you should get a Sig Mk3.
And, that would mean waiting for one to show up. They do come up for sale reasonably often but I can tell you that those who like the CAT preamps, don't let them go easily....

Go back & call/Email Ken Stevens to ask him what the diff between Sig Mk2 & Sig Mk3 is.
Thanks.