I tried the FMC-optical-FMC tweak in my second system in my basement - nothing more than a Powernode driving Elac Debut Reference speakers. The improvement was startling. More air and detail, and improved dynamics. While this system was always musical and enjoyable, the soundstage was always a bit flat. Now there is more air and space around voices and instruments, and percussion and transients seem much more realistic.
I immediately placed an order for the parts to install in my main system (about 6x the cost of the basement system). I'm having a hard time discerning any noticeable difference.
I have different brands of switches going into each system. Maybe the basement switch was more of a problem.