I have owned many Pass Labs amps. Back when I had the Aleph 2 I bypassed outlets and power cords by getting JPS Labs In-Wall AC cable and running two 15' lengths directly from separate 20 amp circuits on my panel through the floor and terminating them into Furutech IEC contectors and plugging those into the amps. I guess these are essentially DIY 15' power cords, though they have the benefit of avoiding the outlet, in wall romex and another cord. The drop in noise floor was substantial over the stock Pass cords.
I have used these with the XA160, the XA100.5 and now the XA160.5. It makes a real difference. The latest generation of Pass amps probably has better noise suppression and power supplies than the older Aleph series, so this solution may not be as effect as it was on the Aleph 2. I haven't tried the stock cords through outlets on the XA160.5.