I have used the Bybee's in applications that have made clear differences that I would describe as a lower noise floor with clearer detail in the highs.
I also have heard them make a difference at the positive binding post of a speaker.
Others that have tried them there have reported hearing no difference in that application.
It may be very system dependent as to weather or not it makes a difference in that application.
I have a buddy of mine that produces the Magic Power Cables. They get several different types of treatment including cryo.
They made such a dramatic difference over stock type cables that I started stocking them and selling them.
The MPC-12's are $225. for a 6' cable.
They brought up the low bass response. They tightened up the bass response all around and made for a more open and airy sound stage with great imaging.
It also made a difference that could be measured.
See test results: http://www.thuneau.com/MPC/test.htm
I have been known to send out the cables for people to try too.