Yet another update: while I originally used the Acoustic Revive RLT1 filter on my streamer and then Etherregen, I have now moved it to the Draytek Vigor 2860 router, i.e. right at the entry point of public ADSL. The resultant clean up of soundstage, insteument timbre, attack and decay is simply unbelievable. Very highly recommended.
I have a few Waversa EXT-1 LAN filters (inline filters) and have been playing with different positions in the audio/network chain.
But had not tried it yet where you suggested. This is huge. I had no idea the public cable internet line was bringing so much noise into the house. The weird part is my streamer and TV, which both saw improvement doing this, are two network devices away.
Cable Modem > Cisco Router > LHY SW-6 Switch > Streamer/TV/NAS
I put the filter inline between cable modem and Cisco router, the earliest point in the chain possible.