Looking for Tube Pre-Amp Recommendations

2 recommendations: The first one requires patience and trust because if you can get your hands on one it will be a stroke of good fortune as they only appear on the used marketplace every now and then and to order one new could take several months... I'm referring to a Tube Research Lab: "The Dude" pre-amp. It is one of the very top most musical pre's you will ever know. It conveys the emotion and architecture of the music in a big holographic stage...
It's built like a piece of industrial equipment that essentially can remain "On" for decades at a time (mine is only turned off for other component swapping or temporary system shut downs like vacations, powercord swaps and such).
It comes SE or can be built balanced if you need it to be and also with 2 sets of pre-outs for biamping ( but double check this point because maybe not every one was built this way...). It is essentially 6SN7 based but also has a tube regulated power supply and can be had with a remote volume too...
Keep in mind waiting lists are very long if you still want to have one built (they are all hand made point to point wiring and essentially custom per user)although if you find a used one it can be sent back to the factory for a check up/upgrades but there is still a time factor.
I would consider this a preferred choice if you have time...and patience....but well worth the wait. List is about $6K new these days (though they may be higher than that now or soon) and I think between $4-$5 used...The main point is though, it will likely be the last pre you will need/want/own, for most people. Well worth the effort but your situation/ MMV...
The other recommendation is the Coincident
Line Stage built by Israel Blume...also in your $5k price range and an excellent performer. Open, transparent stage with just enough tube influence to add the much appreciated "Body" to the performers...There is much written about it on the web...take a look and read.
I'm sure you would find either a good match for your SF power 3's ...Good luck.

Looking to upgrade the pre-amp as the Avalon's are either showing up the pre-amp and or it's just not a good fit (it worked well with my Thiel 6's).

What's problem with the sound? What makes you think problem is pre? Avalon sounds very different than Thiel.

I've had SF Power 3SE+ and SF Line3SE+ (mod to the MAX by PCX) and many more SF pre so VERY familiar with their sound.

I have the Audio Research LS27 and it sound very very good outstanding sound stage and dynamic dead quiet noise floor, great sound Pre Amp. Good luck.Tango

I'm posting my Dude for sale on other sites right now. Worried I can better it, but have the itch. It is a very musical preamp and built like a tank as well. Never had a bit of trouble with except the anodize on the front plate which has been replated this year.

Based on the specs I am seeing online for the speaker, I think your bottleneck is the interface between the speakers and the amp. You are making the amp do a lot of work to drive the speakers to a reasonable volume. The speakers are 4 ohms, which increases distortion (in all amps, not just tube amps) and will also reduce power and bandwidth on account of the output transformer in the amp.

I think you would be a lot better off with a speaker that is more efficient and higher impedance. You can do that without sacrificing sound quality. A good example would be a set of Dreammaker 2s from Audiokinesis. They are 16 ohms, and about 95 db, meaning that you would need about 1/8th the power or so to make the same sound pressure, and the Dreammakers go just as low if not lower.

I would give this consideration. You can make incremental improvement by replacing the preamp, but you can have transformation by replacing the speakers. I am not saying the speakers are bad BTW, just that your amplifier does not match well with them.