Audio Research has announced a Special Edition update to the REF 6.  The REF 6SE has several wiring and component upgrades that bring about higher resolution and transparency.  Existing REF 6 customers can have their units upgraded to REF6SE. 

The improvements come from developmental technologies gained during the design of the new Reference 160M monoblock and Reference 160S Stereo amplifiers as well as a number of newer higher specification internal parts.  

The sonic benefits are represented in increased speed and resolution with added accuracy and greater spectral emphasis and timbral purity.  The REF 6 was already the one of best tube preamplifiers on the market and the SE version takes this a step further.  See also the Audio Research website REF 6SE and REF 6 reviews in Stereophile , Positive Feedback, and Soundstage.  

Here is a description of the REF 6SE by Warren Gehl, ARC Engineering Sonic Development Evaluator.