This one is a little less to do with sound and more to do with very fast transfer rates especially on NAS imports or NAS backups. Keep in mind, all your other network devices need to support 2.5gbe which at the moment is pretty rare at the moment. You would only have this if you specifically invested in it throughout your network, otherwise the ports on the STREAM series will only operate at the speed that it is linked to (which most of the time is going to be gigabit).
The PhoenixNET indeed has 100mb due to the simpler chip we are using - and part of the reason for using that cheap is its lower power consumption and the fact it can be powered by an external linear power rail which is actually very rare.
One idea we did have, and it would be interesting to gauge feedback on this, would be that on a software level we could add something in settings where you could actually set the operating speed of the Ethernet port. So, we could have 'audio mode' that throttles to 100mb, a 'speed mode' which enabled 2.5gbe, or a 'balanced mode' that runs at gigabit. You could change these on the fly depending on whether you doing data transfer, or doing critical listening etc.