Unfortunately it appears to be 2.4 GHz only; around the time it was designed BNetzA may have still been discussing the fine points about 5 GHz licensing; (I was investigating using a long range link at work and had to notify the Ofcom man).
its also not a universal panacea for wireless problems as the range is not as large - depending on how big your building is; what is between your router and the receiver and the presence of nearby aerodromes and radar equipment. Many walls in European houses are full with metal studwork that gets connected to protective earth at the electricity meter cabinet - that creates a Faraday cage (block for radio signals).
I was able to listen in to NDR1s stream myself; I have a business grade VDSL connection from a local ISP but it uses the same networks as Talk Talk with less traffic shaping. I don't use the "free" ISP router and this was a desktop on a cabled part of the network.
The cheapest and most effective solution would be to use the cable to the router; but (making a guess that you are of German ancestry and maybe my uncles age range as its an unusual receiver to find in Britain) there must be a logical reason why you have not done so (such as a being in a rented house); or anything set up in there outside of your study/workshop having to be acceptable to
die Frau / Vriendin and you may already spend most of the day fixing stuff so don't want to be crawling around on the floor and in roofspaces etc and dealing with trunking etc.
PS: If you like Schlager music you may also find these streams from NL / DE border areas of interest..
Geheimezender.com • Streams