Flex:
The power cord; because it is on the supply side of the power supply is the only device that must endure the entire workload of the system. For this reason they also create/produce their own brand of distortion when not designed effectively.
I cant give you a number on the reduction in distortion because of the variables;
however, the change is massive especially when one or more is used.
Mechanical resonance is part of the problem but there is an aspect I have not mentioned; all I can tell you is that the design produces negative impedance without the use of resisters, inductors, capacitors; this allows the resonance tuning to be effective.
Sean:
Our direct drive speaker (not a product for sale at the present) is full of proprietary innovations like the ports, driver mountings, support structure which the cabinet rest on etc. The power cords are so critical to the speakers performance it simply will not function with and degree of proficiency without them.