I have tried the EP15A alone and the SP15A powered by the EP15A. IMO, the EP15A made the most dramatic improvements -- quieter background, more detail, way more bass articulation, and a better soundstage.
Adding the SP15A did improve detail slightly, also with a bit more airiness on the high end. The difference with the SP15A is not dramatic, but I find myself enjoying it more. Don't run power amps through the SP15A, though...I tried it contrary the owner's manual suggestion, and it does seem to degrade the performance, so I went back to preamp/CD into the SP15A and power amps into the EP15A.
When the SP15A first came out, it was a special deal for $400-500 if you purchased it with an EP15A. Now that it is $900, I'm not sure if the improvement justifies the price.
Anyway, I think you get a 30-day trial from most places, so give it a try.
Adding the SP15A did improve detail slightly, also with a bit more airiness on the high end. The difference with the SP15A is not dramatic, but I find myself enjoying it more. Don't run power amps through the SP15A, though...I tried it contrary the owner's manual suggestion, and it does seem to degrade the performance, so I went back to preamp/CD into the SP15A and power amps into the EP15A.
When the SP15A first came out, it was a special deal for $400-500 if you purchased it with an EP15A. Now that it is $900, I'm not sure if the improvement justifies the price.
Anyway, I think you get a 30-day trial from most places, so give it a try.