As someone who worked as a scientist his entire career, if I may provide some advice: Just be systematic in your evaluations. Create a structured experimental test plan, and designate a "datum" for reference. That will the "standard" that you compare other switches (optical transceivers, power supplies, whatever) to. Everything else should stay the same in the system, including the range of musical content, when doing your evaluations. It would also be ideal to pick the same time of day when you're doing listening evaluations. Also, bear in mind that every time you "swap something out", you need to allow time for the new device to "settle". Particularly for "100% digital-domain only devices", e.g. switches, optical transceivers, FMCs, etc. For example, for digital devices, e.g. switches and FMCs, any motion or movement induces vibration in he clocks, and these devices don't like vibration at all. This is particularly true for the crap clocks in consumer-grade electronics. The clocks also don't like fluctations in room temperature, so be sure the rooom is the same temperature for all your evaluations. Also, if you switch out cables, e.g. Ethernet, USB, S/PDIF cables, etc., they need time to settle, also.
Have fun!