I've never tried this setup, but read quite a few related posts.
1. My understanding of this setup is that it should be done at the music player side (rather than the NAS, if only one segment is to be isolated).
2. A number of users have reported incompatibility with mismatched 100Mbps vs 1000Mbps ports between the converter and the player. They need to be matched otherwise it wouldn't pass network traffic at all - I don't know if this is true for some models of converters or all of them behave like this.
3. Converter users also report sonic differences with the changing of the power supply for the converters.