Rpg, do you have dedicated lines for your audio gear? If not, this is highly recommended, with dedicated lines and quality outlets you should not need ferrite chokes and the noise floor should not be an issue.
Keep in mind that if your equipment is connected via single-ended (rca) interconnects, the most significant contributor to system noise (assuming your individual components have good noise performance) may not be the incoming power at all.
See the following paper, which explains that since the shields of unbalanced interconnects carry both signal return currents and extraneous ac-related interchassis noise currents, those shields are commonly where noise is introduced. Which can be improved by shortening the interconnects, using interconnects with lower shield resistance, using audio (not power) isolation transformers, sometimes by re-routing cables, and sometimes by the arguably unsafe practice of lifting ac safety grounds.
RPG -- In my previous comment I should have referred more broadly to the return conductor of unbalanced interconnects, not specifically to the shield. My comment and the contents of the paper I linked to apply to all unbalanced interconnects, regardless of whether the return conductor is a shield, a conductor in a twisted pair or braided configuration, or any other configuration.
The quantitative parameters that are involved, though, and therefore the degree of noise coupling that will occur, will of course vary depending on the specific cable design.
Just found this discussion while searching out a problem I'm having with some old MIT Z-Cord IIs...with two very different pieces of gear!
With both a PreSonus 16.4.2 digital mixer and an Onkyo Integra Research RDC-7 surround preamp, simply using the MIT power cord introduces a distinct digital glare to the high frequencies.
Anyone else notice a glare from ferrite-choked AC cords?!
I can make the noise come back simply swapping out the PS Audio power cords for these older MIT ones...