I experienced this exact same result with my power cords in the amp. Have some custom furutech based cords that greatly improved my coincident Frankenstein mono blocks. The same cords made the xa25 sound worse than stock.
Confession of a poor power cord pairing for a Pass Labs XA-25
I recently purchased a Pass XA-25 to replace my Nuforce STA-200. I had replaced the power cord on my Nuforce with an entry level Silnote power cord which made a tremendous difference in sound for the Nuforce. However, when I received my XA-25, I apparently was in an extreme hurry and did not install the cord that Pass Labs included.
This evening as I was sorting through a big box of interconnects and power cords, I discovered a power cord that still had its factory twisty tie intact. After a few minutes of deliberation, I realized that this was the power cord that was included with the XA-25. I hooked it up and wow!.. Detail and Bass that I didn't know this amp was capable of.
Moral of the story.... Just because it's factory power cord.. doesn't mean it can't be good.
This evening as I was sorting through a big box of interconnects and power cords, I discovered a power cord that still had its factory twisty tie intact. After a few minutes of deliberation, I realized that this was the power cord that was included with the XA-25. I hooked it up and wow!.. Detail and Bass that I didn't know this amp was capable of.
Moral of the story.... Just because it's factory power cord.. doesn't mean it can't be good.