I've always liked the Audio Research house sound, and looking into the 10 pre - reading this thread has been really illuminating. Thanks to everyone for your impressions.
I remember listening to an Audio Research amp and pre for the first time, literally a day after they arrived at my local dealer, who had just started carrying the line.
I was less than impressed. The treble would occasionally leap up and bite, and the overall effect was wooly in the lower midband and bass. I left, surprised that they would charge that much for the pair, as frankly my own less pricey tube gear sounded far better.
Fast forward six months later, and I returned to the same dealer - and those ARC boxes were playing in the same room. They sounded completely different - absolutely beautiful, with an extended and sweet treble, and a new clarity to the mids and bass. I couldn't stop listening for at least 45 minutes - they were hooked up to Wilson Sabrinas and sounded perfect, without deviation, the entire time.
I asked a staff member what happened, and he smiled nonchalantly. "Oh, they just finally broke in - all the ARC stuff does that, to varying degrees." He told me to prepare for a good 500 hours of break-in time, and they will reward your patience. That is so true for this particular line - it is a profound night and day difference.