I have added the GOR-b between the P-03 and D-03 after more than a year using the two alone. It is really hard to say what, specifically, it does, except that when you remove it the naturalness of the sound is diminished, and even superb CDs and SACDs become excellent digital sound again, not just excellent sound. I have heard from a very reliable source that the G03x has little positive effect between the P-03 and D-03, but is a substantial step forward when used with the P-05 and D-05. If, after my own experience, I were going to get a P-05/D-05 combo for a second system, I wouldn't even consider it without an Esoteric clock, the best I could afford.