I'm with the buy �200 worth of music and you'll get more enjoyment vote.

As has been said SpeakerLink is not Ethernet even if the same cables and connectors are used.
You don't know what is connected to what inside this device.

If it filters noise at what seems to be 5KHz according to the images, what effect is it having at higher frequencies. The answer will not be none.
Whilst SpeakerLink runs at lower frequencies than gigabit ethernet for sure, the edges of the signals are the critical part, messing with these will potentially introduce unwanted jitter and other audible timing related artefacts which despite Bob Stuarts most excellent work with PLLs in this area, you most certainly dont want to increase in the first place.

G61R, 5K5's (fronts & centre), 5K's (sides & rears), D2500, JVC DLA-X70, QNAP, Roon(Pi)