Sean, I have read all of the way through your thread on this and see that I was involved during the early days.
You seem to have a unique problem with the incoming BT router installed in your garage and not your home where Bartok is situated.It appears thereon to the home you use wifi. At least Roon gives you access to Tidal but this really does not seem to me to be the answer that you need or are looking for.
Potential solutions seem to have been offered and there may have been some directly from dCS but naturally I could not see that side of things. So you seem to have ended up with a work around suggested after a visit from your dealer. As you have deduced Bartok really needs to be hard wired to the router as it is not a wireless device.
Can you not get BT to move your connection so that the router is in your home?
As you have written to dcS about a Bartok Apex upgrade they have , naturally, said that such a product has not been announced. Which it hasn’t although rumours abound. However in the context of Mosaic, Apex upgrades offer nothing in this area. Apex is a hardware change concerning (briefly) power supplies, DAC and analogue output stages. It has nothing to do with the streaming board. So there isno solution there for your issue.