Preamp recommendation please..

The amp has an input impedance of 100k ohms.  That opens up the field to include most tube pre-amps. 

My suggestion is to try to find a used Herron VTSP-3 even if it might be a little above your budget.

An alternative would be a Herron VTSP-1. 

Keith Herron can bring both up to the latest specs and even take the VTSP-1 far beyond its original performance.  The VTSP-1 at the current mod level is quite good.

I would look for a Krell EVO 222 preamp!  CAST is incredible.  CAST cable at 1.5k pair sounds better the XLR cable at 10k pair.  There is a speed, resolution, coherency to CAST that is one of Krell's ace up their sleeves.  The EV222 ought to be around your budget too.  The even better EV202 (2 chassis) preamp might be found at a steep discount that's close to your budget...maybe?  Krell power amps sound especially good with Krell preamps.  

I can recommend two preamps that I am currently using. The Roague RP-5 and the sonic frontiers line 1.I also like a tube preamp with A solid-state amplifier.

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.