Tweaking Cary SLP-98P F1 Preamp

As you know for SLP-98, the F1 mod is a significant improvement over the standard. I just bought one used and the stock 6SN7 tubes that come with it are horrible. So, I am waiting for WE6SN7 tubes for it. Until it arrives I want to ask people with experience with F1. I have Pass X350.5 amp driving Soundlab ESL speakers.

1. How good can it get with best tubes?
2. Some have recommended using NOS 6f8g/adapter instead of 6SN7, any thoughts?
3. After getting the best tubes, is it still worth it to direct-couple it? It is supposed to improve bass, dynamics....
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Do you put them under the preamp's feet or under the chassis?
How do Rollerblock Jr compared to something EVP blocks for isolation?
You put them under the chassis.  I have not used EVP blocks but I have compared the Rollerblock Jr's to BDR cones/pads, Isoacoustics Orea's, and Golden Sound ceramic cones.  Rollerblocks were clear winner in every case.  Plus they aren't terribly expensive (compared many other products) at $225 for 3.
I have a Cary SLP-98 F1 in my big system. I have not rolled any tubes yet. It's not the last word in pre-amps but it is still a very good pre-amp with some musical leanings. It should work well in your system but if you are looking for more accuracy and perhaps more detail a top of the line Audio Research will push you in that direction. I personally like the sound of my SLP-98 and don't have any plans to replace it.  
...I personally like the sound of my SLP-98 and don't have any plans to replace it.  
Me too. Nice outboard power supply, and with top shelf 6SN7s, upgraded coupling caps and rear wiring, using quality OCC interconnects, performs as well as I'll ever need.