Preamp recommendation please..

I bought a used Classe CP-65 used more than 5 years ago and I have never felt the need to change. I think it's great. You can probably get one used for between $2000.00 and $2500.00 

I use a Schiit Mjolnir 2. For the price you can buy it, a bunch of different tubes, and still fall back on solid state if you want.

http://schiit.com/products/mjolnir-2

Krell power amps sound especially good with Krell preamps.  

CAST is incredible.

I 've heard this in the past.

I also read that Audio GD has a great preamp (Master 1).. quote from their website:

Master 1 is compatible with KRELL amplifiers.
A cable can be made with one side connecting to Master 1 ACSS outputs, other side to a KRELL amplifier CAST inputs.
The ACSS output pins:
Pin 1, GND
Pin 2, Hot
Pin 3, Cold
KRELL amplifiers have lower gain versus audio-gd Master series amplifiers when using the CAST connection, so customers can custom order the Master 1 to have higher ACSS output gain if expecting to connect to KRELL amplifiers.

Costs under $2k, including tax and shipping costs.

Happy to hear any comments about this option.

Don Sachs builds the finest-sounding (and looking) tube preamp I have ever heard.
http://www.dsachsconsulting.com/custom%20line%20stage.html
For <$2k it comes with the top-grade silver/gold/oil Mundorf coupling caps that will handle any solid-state or tube impedance inputs, XLR balanced input, and superb master and channel pots and source switch. I have mine populated with metal-based MELZ 6H8Cs, and NOS RCAs, though any good NOS 6SN7 Sylvania or RCA works fine in them as well. These are built pretty much to order so expect a few weeks' wait for delivery, but well worth it. Don is located in Nelson, B.C., but through an arrangement with Canada Customs he drives over the border to the U.S. for weekly shipments so no duty charges or hassles with Canada Post. I finer preamp you will not hear.

Hands down "First Sound".  I have the Mark 3.  It fronts a Conrad Johnson Premier 140 with Teflon upgrade.  I had listeners over last weekend.  I actually sold one my CJ amp.  I have the Sonus Faber Luito 3 way floor standing speakers ($5,000).  The buyer has the Sonus Faber Guarneri ($22,000).  He along with the others were absolutely floored by what I was getting out of my system.  Blown away by how powerful, musical and relaxing my system is.   I know a huge part is the First Sound preamp.  I had Airtight and Mcintosh preamps before the First Sound.  No comparison.  The depth of base, clarity, musicality, consistent tone from top to bottom.  It is just so nice.  It also uses a pair of 6922 tubes so you have a little room to shape should by using a Telefunkin, Siemens, Bugle Boy or GE5670 tubes.  Emmanuel the owner of First Sound has come to my house twice and helped me to understand how to really tune my system.   That also helps it to stand out.  He is one of the nicest and honest people I have worked with.  The preamp is also highly upgradable.  The basic chassis is already designed around a mono platform.  The power supply is external.  If you get a second power supply the unit is true mono.  From there you can upgrade the stepped ladder attenuator, capacitors and some other parts.  I have the base unit and just don't see how I could need anything better.  I have seen used units for $3,000 + or -  on Audiogon.  The attenuator is based upon resistors in a ladder.  Only 2 at any one time in the signal path.  This is considered the best way to control volume.   If the volume is not working correct with your amp, Emmanuel is very good at building a new one to meet your needs.   See his website for a better understanding of what he offers and pricing.  If you see a used unit, call Emmanuel and see what he can do to bring it up to snuff for you.  You may need to do nothing.  I have a friend with a stock Mark 2.  He loves his unit and sees no reason to upgrade it.  Try one out.  I think you will hold onto if for years.