There are many who prefer the SP-10 (which I recall is a two-chasis unit) to the SP-11 in their MkII versions. The SP-11 was more neutral and had better deep bass, but certainly lacked the tube bloom and dimensionality of the SP-10. I had an SP-11 for 4 years, it was the first high-end preamp I'd owned. Back then, I was slowly being weaned from solid state to tubes, so I probably would not have appreciated the SP-10 as much as I do now. A classic case of tube vs. (hybrid) solid state preferences, I guess; your taste would decide which was "better". From the prices of used 10s and 11s, I'd say they're both held in high esteem by audiophiles. The SP-9 was ARC's attempt to make a budget SP-11 hybrid, and in its MkI version had mixed reviews; it certainly did not have a tubed preamp sound. I can say that the SP-15, which was the SP-11's replacement and had half as many tubes as the SP-11, never seemed to have the critical or popular success of either the 10 or 11. By the time it came out, I was growing enough in my appreciation of tubed equipment to prefer my SP-11 and resist upgrade fever. Had I been into the high end earlier and owned an SP-10, I probably would have resisted the urge to get an SP-11 as well.
