here's a couple of review links that compare the 2
http://www.theabsolutesound.com/articles/audio-research-introduces-reference-6-line-state-preamplifi...
http://positive-feedback.com/reviews/hardware-reviews/audio-research-ref-6-line-stage/
http://www.theabsolutesound.com/articles/audio-research-introduces-reference-6-line-state-preamplifi...
http://positive-feedback.com/reviews/hardware-reviews/audio-research-ref-6-line-stage/