Audio Research Preamp with Cary Amp?

The F1 is Upscale's proprietary branding, but you can order the same pre-amp modification through any Cary dealer or send you existing pre-amp back to Cary for an update. 6SN7 tubes are not that expensive with a nice pair going for around $65/pr up to the best available at $250/pr.

Ok then, it's unanimous. I think I'll go for the Cary pre.

Since we're on the subject, what would you guys recommend for 6SN7's? Based on what I've read are shortcomings of the 98, I would be looking for more extended highs and tighter, more extended bass. Is there a tube out there that can do this?

Thanks

Having the SLP-98 directly coupled will give you a faster pre-amp with extended highs and tighter and deeper bass, less tubey sound. Tubes that I know work well in the SLP-98 are as follows: Order of preference.

TungSol black oval (round) plates, blackglass, oval mica (very expensive)
Sylvania 6SN7GT blackplate bottom getter 1950-52 "Badboys" (expensive but can be found for a decent price if patient)
6H8C Russian Military 6SN7GT metal base (well priced excellent performance)
Sylvania Tall Boy 6SN7GT (great value, great tube)
Sylvania VT-231 (for $100/pr, a no brainer)
Ken Rad 6SN7GT - VT-231 JAN (same as above)

If you are buying from Upscale, last I checked he still had some of those Popes from Holland 6SN7's. They are phenomenal.
I hate to throw a wrench into the discussion; but I didn't like the SLP-98 with the 805's (the ones I heard it with were the AE's). Too much constriction, IMHO. I heard a Heron Audio VTSP-2 replace it (the 805AE/98L combo was in the reference system at a no-longer-in-business hi fi store here in Phoenix) and it was much better. On a side note, the SLP-05 was better suited to the 120S or 211 (run balanced). It made the 805's magic midrange a bit sterile sounding.
Some linestages I'd consider are the Dehavilland Ultraverve or even the Antique Sound Lab Flora. Both are awesome. Open and neutral; but tube neutral.
The F1 upgrades would make the 98 faster and more neutral; but I doubt they would remove the slight constriction issue.

In all honesty I think the result of the choice will be a total system pairing highly dependent on how you percieve your speakers sound. I use a Cary pre with uber 6SN7s, the famed Ws, into tube power amps wich are Opera Consonance Cyber 800 monoblocks using 6CA7s outputs tubes. While they are definitely not the tubey, slow, syrupy, tube amps of yesteryear, I was concerned that the combination might be too much. However my speakers are JM Lab Focal Electra 936s which tend to be very detailed and analytic. The result is sheer nirvana for me anyway.
Now I strongly recommend tube power amps and tube preamp but I also think there is a place for good SS preamps because I am convinced it is the tube power amp that really matters. If your speakers are warm, polite, British style laid back etc. You might find greater synergy from the ARC or even a good SS pre.
I am saying this as an ardent collector of 6SN7s. They have the best tone IMO of all preamp tubes but the gear you use with them must be relatively clean.
Also watch out for microphonics in 6SN7s they are prone to suffer this problem when buying old stock. It is almost unavoidable, however a tube which is noisy apart from microphonics is not part of the deal. The noisy tube should be returned to its seller without question. Some will accept returns of microphonic tubes if you can get them to represent them as "Phono" grade or just non microphonic prior to buying them. Always ask if they are quiet non microphonic ubes first. I am fortunate to owm massive brass 6SN7 tube damper which alleviates rge microphonics. I don't think they are made anymore .