Seeking Suggestions on Preamp Upgrade (CJ, Aesthetix, EAR)

David - there is a VAC Ren Signature on the A-Gon listing right now that would be perfect with your PASS and fit your budget easily as well.  Do NOT hesitate as this is a great pre at at great price (no affiliation, just a very happy VAC owner)

Unsound and jperry:

Thank you for the insight on the impendence matching between the source and load.  I read some on-line information on this topic.  It appears that the the 1 to 10 ratio is related to balance between the maximum power transfer and system power efficiency optimizationis.  Back to the actual impendence readings for each brand listed above, none of them can meet the requirement for the rule of thumb, c-j's output impendence is less than 500ohm, and barely 100ohm for ET5, interesting perspective.

thank you again.

Did you eliminate VTL's 2.5 and 5.5?  I've been very happy with the 2.5 for many years with a McCormack amp. Lush and non fatiguing.

Oh my, this question is a delight to which to respond.  I am a long time customer of Don Sachs who produces a 6SN7-based custom-made tube preamp in a beautiful wood cabinet.  By far, it is the finest preamp I have had in my 45 years of having good to great gear.  Don offers lots of options including a remote control, XLR connectors, caps upgrades from Mundorf Silver Oil, Jupiter Copper, to Dueland caps that increasingly enhance the performance of his preamp.  The basic preamp runs around $1800 and betters the performance of preamps many times the cost of his preamp.  Google "Don Sachs Consulting" for more information.  This is my highest recommendation for a preamp.  

HI
Don Sachs here.  I see I have been talked about.   I would love to build the OP a preamp, but he has an amplifier with a 15K input impedance.  I could certainly use a really large output capacitor value and drive that load, but it has been my experience that the sp14 design, while a fantastic preamp, has some issues driving loads less than 30-40K input impedance.  It will do it, but sometimes may not be as dynamic as people want.  I would say this may apply to many tube preamps.  Really, I recommend my preamp for loads of 47K or higher.  It will work with anything, but sounds best with a more benign load.  Any tube amp in the world is 70-80K or higher:)

cheers,
Don