Audio Research sp 11 compared to the sp 10

Am looking for an AR sp 11, but have had no luck. There's a sp 10 on ebay (plus a sp 11 that has four days left) The sp 10 is still under $1100 with time to run out tomorrow. What's the difference between the two AR pre-amps? Is the sp 11 that much better than the 10? TIA
Dave