Question on the Purist Audio Limited Edition P/C's

.....I first added one of these power cords to my amp and yes there was a noticeable positive sonic difference. I just added a second one to my pre-amp and that too made a positive sonic difference, however, not as much as when I added one to the amp. So, my question is, is there a diminishing return when you add more of these very expensive power cords to your system ???? I still have a dac and transport and was wondering whether it would be sonically worth it to get two more and round out the whole system with them ??? I would appreciate answers from Audiogon members who own and have these cables in their system. Thanks ..........