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

@smodtactical I've built two SP14 preamps using the tubes4hifi.com boards.  You can build it for less than $500 including upgraded capacitors.  The build is quite straightforward with building and wiring to the chassis the biggest pain.  The SP14 sounds very nice but it doesn't outperform my heavily modded Cary SLP-70 although it comes close.  I have yet to succeed in building a SP14 that is completely quiet so that will be a problem if you are planning on using it with efficient speakers or a high powered amp.

I have a BHK Pre and I do not call it warm. Now, I've only used the PSVane factory Tubes and Gold Lions (12au7). The PSV tubes are slightly warmer sounding. The BHK is neutral but "silky" with the tubes I've tried. 

You have gotten a lot of good input.  I was in a similar situation to you recently, looking for a tube preamp to mate with my Pass XA60.8.  After much research, I decided a 6SN7 based preamp was what I was looking for.  That led me to the Aric Audio Motherlode.  Aric worked with me to make it truly balanced with some other enhanced performance qualities.  As a result, the Motherlode XL is now an offered product just slightly above your price range.  

Over the years, I have owned ARC Ref 5, Pass Labs XP22, Doshi Alaap, McIntosh 2500, and Lamm.  While they were all good in their own way, I found each to be lacking in some area important to me.  The Motherlode XL has all the qualities I was looking for and has overcome what these other preamps were lacking (in my opinion).  It is very dynamic and punchy, very detailed throughout the audio band, big deep soundstage with clearly separated images, beautiful tone, and dead quiet. It took my system one step closer to sounding like real live performers.  While I'm still exploring 6SN7 tubes, it is easy to hear differences.  For example, using Hytron 6SN7, it is warmer with softer transients.  With Sylvania Bad Boys it is more neutral and dynamic.  

Most importantly, it mates beautifully with my Pass amps.  No hum, buzz, or tube noise at any volume level.  It is handmade in the US and working with Aric was a true pleasure.  He will build it to your specifications and recommend various tube combinations to suit your taste.  

I didn't know much about Aric Audio before this, but he deserves all of the accolades he is getting on Audiogon and in professional reviews.

Good luck and have fun in the process!

Dave  

 @tricon_dave  High praise for Aric indeed. I was actually going to go with the motherlode before ending up with the ref5se. In hindsight that probably was the better choice for me sonically. Aric is a super nice guy and I love how transparent he is about his builds and what components he uses.

@smodtactical upgrading to the GE 6550  is supposed to be smoother and wakes up your AR ref5SE preamp a bit, assuming you are still running the stock tube in that spot. Call AR and ask them about how they use to reference the expensive 6N30P-DR / 6H30n-DP Super Tube in their amps. Some like to replace both the 6550 and the 6H30s.  For Plan-B, maybe there is more to be had out of your current preamp before leaping away. Best of Luck.