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

Hi  david, 
you have asked an open question. Soon enough, there will be just about many different preamp recommended to you. 
what is your music genre and your sound preference like? i.e laid back, relax? euphoric? vivid? big voice , wide soundstage?

there are many different preamp that will be good only in certain aspects of audio reproduction. It's very difficult to achieve absolute detail with richness and tonally accurate plus wide open soundstage if you listen to majestic performance like in a classical recording. only a handful with a heavenly price tag  preamps can do well in everything.
-phil

Hi, Phil:

Nice suggestion.  My original intention is to confine the discussion within very few items based on the paper study I did.  I have omitted some very obvious major brands based on my first-hand experience.  I prefer a warmer sound, with laid-back, live-like, classical music remaking.   I go to live concert performance pretty frequently.  To me, a lot of equipment sounds too bright and too articulate to mimic the string groups in an orchestra.  Of course, this is only to me individually, and may not be applicable to majority.

My current system is free of listening fatigue - I can do a continuous listening for hours with peoridic performance or harpsichord of Baroque music.  But to compare to a live performance, there is still a distance.  I am not talking about personal emotional involvement, just pure acoustic quality.

I cannot afford the heavenly price tag equipment.  Just acoustic sound of classical music of natural sound, so the bass requirement (I rarely listen to music played by organ) is not very demanding but mid-range and high frequency may be my major concern.

Thank you very much for posting to clarify the purpose.  

FYI:
  The prevailing rule of thumb is that the input impedance of amplifiers should be 10 X greater than the output impedance of  preamplifiers.
  The Pass XA30.5 input impedance is spec'd at single ended: 15K Ohms and at balanced:  30K Ohms.
  c-j recommends an amplifier input impedance of 20K Ohms for all of the above mentioned c-j preamps. All c-j's are single ended only.
 The Aesthetix Calypso suggests recommended amplifier loads of single ended:  10K Ohms or greater and balanced:  20K Ohms or greater.
Couldn't find anything specifically re: the EAR 868, but Ear does suggest looking at the EAR 912 as this what the 868 what based upon. The EAR 912 output impedance is spec'd at:  600 Ohms.
 The Zesto Leto  output impedance is spec'd at:  150 Ohms both single ended and balanced.

What you need is to purchase a reasonable good preamp that response well to tube rolling. Most people use tubes to fine tune the degree of warmth.

EAR , Mapletree audio and Joule Electra are some of the tube pre that i find may have more warmth compared to CJ , ARC, Allnic and alikes.. do be aware that within its product line, there are also some difference in their sound characteristic too. PrimaLuna is another suggestion, however, personally i feel it's does not sound laid back, much better for music with singers. 

you have to judge for yourself how distant sound you feel that's right for you. There are many preamp that provide warmth but it's much more difficult to strike the right balance mix of detail, articulation and warmth that suited to your taste, hence tube and cable rolling sometimes can be quite handy. 
-phil

Make sure the impedance matches as suggested above by unsound, and weight your opinion about responses you receive toward those from users, as opposed to those that have not owned or used the equipment they are recommending or disparaging. 

My general opinion is that if I have not heard it I can't have a valid opinion on how it sounds.