Someday soon I hope to take my Continuum 500 over to Soundings and compare it to the 501 with and w/o PC1 and the 312, but I haven't done it yet. Lacking a direct A/B, all I can say is that they're very much alike. I'm never struck with the feeling of, "oh I wish I had that" when I go from one to another in slightly different systems. Still, in most A/B situations you will hear some slight differences. I'll be glad to report when I can, but I have nothing to add right now.
Dave
Dave