Looking for warm tube preamp (should pair well with Pass power amp), budget $6000

When I had recently received the Freya and festooned it with NOS GEs (a while back...maybe 132 years?) some friends and I had a little shoot out festival with a couple of ARC tubed preamps (one was a "reference" model), a Cary SLP 98, and a VTL something...my Freya stood its ground against all challengers and amazed the gang of audio geeks as a FAR less expensive alternative to the other precious items...possibly why its in Class A now. 

@decooney

Re; The Cary SLP-05, I have not heard the ultimate upgrade but everything you mention about the SLP-05 is right on. Cables and tubes can make a huge difference.

The other important factors are gain adjustment, rectifier and balanced inputs and outputs.

Gain adjustment is critical for having the cleanest and the most dynamic sound. There seems to be a large tolerance but it needs to be considered and not just cranked all the way as a default.

The 5AR4 / GZ34 rectifier can be upgraded to a NOS f32 made by Mullard off label for ~ 150.  Best 150 I have ever spent- more open and dynamic.  

I recommend using the balanced connections if at all possible, especially the balanced out to the amp even if the amp is single ended, use a neutrik adaptor.

the dynamics and sound stage are so much better using the balanced out vs. the single ended. not even close !

I also have a Zesto Leto.   It is an incredible sounding piece.  Zesto support is top notch,  I just had George do the ESP power supply mod.   It replaced a Conrad Johnson Classic 2SE , the difference was pronounced.    The Zesto is so life like , it is voiced perfectly.    If I had the cash, I would buy the latest Leto II Ultra.   Best sounding component I have ever owned , used ,or demoed. 

@avanti1960 Based on what @decooney said I feel I might actually really like the Cary sound.

@smodtactical  many of the nice tube preamps mentioned so far could be good, even better with upgraded tubes and higher quality caps in them.  Some providers offer their own optional upgrades when purchased new. Or, when buying used components, finding a good local tech to install / test common upgrades can be another recommended option for consideration. Watch out, replacing and hearing a better quality tube or a better quality cap, can be addictive for all future components. :)