Preamp recommendation please..

First Sound products are 'end of search' pre amps.   

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.