earflappin,
you said: As I noted in another post, I tried an optical Firewire extender - found it made no audible improvement - then learned after I sent it back from the manufacturer (should have checked in advance...oh well) that it simply re-transmits the electrical signal so any HF noise on the line before the optical transmitter/receivers passes through.
Any noise that would "re-transmitted" over the optical link is irrelevant to the phenomena that you are investigating. I actually don't really believe that it is "re-transmitted" anyway, since optical Firewire is fully regenerated via a PHY from a local clock in the repeater. Any noise that would be injected in the data lines would either be irrelevant or sufficient to corrupt the data. If it corrupted the data, there would not be subtle changes in the sound -- you would just have substantial dropouts. The only mechanism I can see that would have an effect on sound quality would be noise injection onto the ground of the converter via the FW ground line, but in any case, the optical connection would have isolated any potential ground contamination going between the MM and the LIO-8 via FireWire, so it would have isolated any relevant noise source that was transmitted via the FW connection. Since it had no effect on your system, that tends to indicate that the source of the issue that you have identified is not entering the system via FireWire, but rather through the AC power distribution system and is probably occurring at your power amp.
You could try using your iso tranformer on individual components rather than the MM and see if it has an impact with some specific component (e.g. amp or LIO, etc.)
Best regards,
B.J. Buchalter
Metric Halo
