Preamp recommendation please..

I have the Modwright 35.6.  I am using the set with Pass Labs SS amps.  Sounds amazing! You could start with the single box, then upgrade to with the power supply 2nd box later.  This will allow you to have a good preamp now and a reference preamp later. The best of both worlds.

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.