Thanks for your thoughts!
Yes, Chrissu got it right – the idea was to swap the other switch with the Cisco. For several reasons, I did not do it:
1) With the Cisco in the cellar (where the TP Link switch is now) , there would be a number of cables, plugs and inlets between switch and streamer compared to only one cable with the two corresponding interfaces in the present setup, where the Cisco switch is as close as can be to the streamer.
2) As central switch in the house the Cisco would have to handle all the other traffic that is going around in our house too. Now it exclusively manages the audio stream and nothing else, so in a way it is isolated from the rest. Probably setting priorities for audio stream via QoS settings might address this when acting as central switch for everything, but I'm not capable enough to do this. Also I would fear that the much heavier traffic load might also stress the PSU resulting in noise and more work for the PHY chip.
3) I guess a general purpose switch should have all Gigabit ports so I would have to go for the much more expensive recent Ciscos.
4) I asked two dealers that sell the "audiophile" Aqvox Switch how they would implement their switch in my configuration – substituting the existing central switch or adding it as close as possible to the streamer. Both independenlty from each other clearly suggested the latter.
So I'm going to leave it as is...