Using a FMC in front of an OpticalRendu improves the sound by a little bit. I have 2 OpticalRendu’s in my office hooked up to 2 DAC’s, which are both connected to a Benchmark LA4 premap (and 1 DAC also connected to a tube amp).
I am able to do some side-by-side comparisons very easily. Especially when I use the GROUP stream option in ROON. One of my Optical Rendu’s does not have an FMC in front of it and the other one does. The one that has the FMC seems like a cleaner window into the music. It is not a lot but worth investigating since an FMC is not expense.
Only problem for me with FMC’s is 2 of them failed on me (cheap ones) so I am now using a spare EtherRegen in reverse order as an FMC. I think any reliable FMC will suffice.
BTW - The idea of using the FMC in front comes from Jon Swenson, the designer of the EtherRegen and OpticalRendu.