In summary I found a correlation between the inter frame timing consistency on the ethernet and the sound signature on the legacy streamer. The more consistent the spacing between the frames, during the media transfer, the more I seem to prefer the sound. The greater the variation the less i found the sound appealing.
This led to experiment further and I discovered the benefit of the internet streaming proxy media server with services like Tidal - it seemed to vey much improve the sound as it made the inter frame timimg look and sound like it was being locally streamed.
The timing consistency seemed to be a product of the hardware, operating system and to some extent the application working together.
The most consistent timing I found was from a Netgear RN102 running its internal DLNA server - and that sounded the most preferable on my system over the other platforms and other applications.
I created some wireshark macros to explore this further. Look at the red line which is the minimum time between frames in media transfer bursts
An Example of Minimserver on RPi
An Example of the DLNA Server on a RN02
In these examples the latter sounded preferable on the legacy streamer.