I had a SP-9MKI for a short time and then moved into the ARC SP-15. I have been very pleased with the SP-15; especially since I put NOS Tubes in the phono section. The NOS tubes not only sound better, much better, but they also last much longer. I espouse the integrated phono preamp/preamp. Less issues with coloration due to interconnec cables between boxes and less risk of noise. The SP-15 is fairly quiet because it has a seperate power supply box- as many good preamps do. It also has plenty of gain for low output MC phono cartridges with a handy cartridge loading dial on the front plate. I have heard the Ref 3,5, and 40th Anniversary preamps with the PH7 and Ref 2 Phono preamps in other systems and I don't feel like I'm missing much. It would be a differnt story, I'm sure; if I heard one of those more contemporary preamps in my own system which I know so intimately.
I sent my SP-15 preamp into ARC a few years ago for a tune up. A connector went bad in my umbilical cable between the two boxes, which was wierd since it just sits on a shelf. So they fixed that and per their recommendation, replaced all of the electrolytic capacitors in the power supply section for me since they were getting a bit aged. Other than the umbilical cable issue the SP-15 has been a great sounding, reliable workhorse for me these past 11 years.