Best amplifier for Acoustat 2+2 electrostats for holographic sound, or change speakers?

@tomic601 agreed those Korg tubes were microphonic in my experience with them B1 as well.

I have heard Microphonic and I have heard the measures put in place to control the audible effect.

When controls are in place, there has been nothing present for any length of time to cause any concern.

The Pre' has made such an Impression on myself used as loaned models in my system, I have purchased Bespoke PCB's with a option to have oversized components added, there is plenty of real estate.

There is also Bespoke Built VC's to be used with the Monoblock Balanced Pre' I am having Built.

The Casing is to be Airtight P'holz and the Nutube will, as an additional measure  be embedded into its own P'holz Sarcophagus.

A selection of the local HiFi Group, as result of the Nutube DHT experience, are now experimenting with Tube DHT Pre Amp's. Speakers being used are Active Cabinet, Passive Cabinet, Horn Loaded Cabinet and ESL. 

I was given my first experience on Wednesday morning in a very well known system, where the CD Source > Valve DHT (gain matched) to a Neurochrome Power Amp > Passive Cabinet Speakers .

This was the best I have heard this system being driven by SS Power Amplification.

There is also a Design coming together to modify the Valve DHT, something about the methodology for heating/driving the Tubes. 

My visit to this home prior to this visit was listening to the System via a Heavily Modded SP10 (Bespoke Speed Control / Platter Bearing Overhaul) > Bespoke Built TA > Newly Refurbished AN IO > Heavily Modified design for a KB1 (Three Box with - Blackgate Cap's - Bespoke VC)  > 300B Power Amp's.

Hearing this set up in use was also an indelible experience. The new encounter with Valve DHT and SS has been quite different as an impression made, but both are equally indelible.

The time will come when everything is modded to its end point, and the side by side comparisons will commence. 

Note: When the EE goes down the path of modification, the Base Model is maintained and Modification Models are built from scratch, these are then easy to discern where the Plus/Minus points are discoverable.      

I may be asking the obvious, but if your Acoustats are not up-to-date in terms of available upgrades, they may not be operating at their peak potential.  I had my 2+2's upgraded by Roy Esposito (formerly of Acoustat) back in 2013.  Completely rewired the interfaces with mono-crystalline wire and replaced nearly all the other components, save the medallion transformers.  Also opted for the "Air" upgrade, which provides a manual switch to by-pass the high frequency adjustment pot.  I use a Mark Levinson ML11/ML12 amp/preamp combo to drive mine; totally coherent, detailed and transparent.

The cost of the Acoustat 2+2 upgrade in 2013 was $550 including return freight (outbound freight is on you).  Meets your budget criteria, if they have not already been brought up-to-date.