good thread guys.
I'm an Etherregen user and I feed it with optical from a Cisco 2960. Adding in the optical was very noticeable.
I have a cheap Chinese 10mhz clock on the ER. That does make an audible difference.
I too am drawn to the simplicity of passive network acoustic filters. I might be up for trying the pro this year.
I have very good power supplies (Ferrum Hypsos on the ER and a long dog audio LPS on the clock.