Yeah, right now all these things are just trial and experimentation. It'd be good to see what the final EtherRegen looks like and what John Swenson or Alex can tell us about their product and provide any measurements / white paper.
I've also tried different switches and spare routers (D-Link, Trendnet, and Cisco Linksys) with stock power supplies and a Teradak linear power supply. I have both gigabit and fast ethernet switches. With the BDP-1, the connection to the BDP-1 is always 100 Mbps. However, using gigabit vs. fast ethernet switch can modulate the connection speed of other devices like a NAS or computer. Using a fast ethernet switch on the BDP-2 and BDP-3 would slow down the BDP's connection from gigabit to 100 Mbps.
John Swneson on why EtherRegen will have a 100Mbps on the clean port meant for use with audio:
"Why is the clean output 10/100 not gigabit? Because it is much cleaner to do so. A significant amount of jitter on a Ethernet cable come from noise on the power/ground (PG) networks inside the chip. The more stuff is going on and the faster it is doing it, the more noise gets generated on the PG network. Gigabit has way more stuff going on inside, thus generates a lot more noise, which causes significantly more jitter. By keeping it down to 100 the clean port has much lower jitter."https://audiophilestyle.com/forums/topic/38968-etherregen-early-general-details-we-are-late-but-getting-closer/page/2/?tab=comments#comment-802257
Although I remember once reading Ted Smith of PS Audio urging to use gigabit for the rest of the network to keep jitter down if it theoretically mattered.
I also find it interesting that a lot of users now like the NAS option. I remember in the first few years of the BDP-1 release, the USB option was always preferred over the network option by both users and review magazines. Was that a result of changes in the BDP software or people's sonic preferences changing over time? While it's partly useful to hear from users what method they prefer for listening, it'd be even better if they described how they hear the various playback methods sounding differently so it'd provide context on what they consider as sounding better or worse. Someone's better could be someone else's worse.