I've used most of the upper-end Shunyata cords with the Atma-Sphere M60s, MA1s, and MP1, all with excellent results.
However I'll agree with the other long-term Atma users on this thread - the amps just are not that finicky wrt power cords and don't think you need top-of-the-line to reap their benefits. If looking today I'd consider the 9AWG Shunyata Venom HC which is somewhere around $300.
The best thing you can do for these amps is dedicated circuits and keep any DC out of the line.
However I'll agree with the other long-term Atma users on this thread - the amps just are not that finicky wrt power cords and don't think you need top-of-the-line to reap their benefits. If looking today I'd consider the 9AWG Shunyata Venom HC which is somewhere around $300.
The best thing you can do for these amps is dedicated circuits and keep any DC out of the line.