I was assuming that the Spotify streaming was done by a Windows computer, rather than, say, a mobile device. Windows probably negotiates a codec with the Bose then sends the audio, via wifi or cable, to the Bose - via the router.

If the computer and the Bose are both on wifi then both the streamed router-to-Windows input and the Windows-to-Bose transmission will compete for the wifi. If the wifi is poor that might struggle. Just speculation.

What does it sound like on the desktop's soreakers, if there are any?

We have 2.4GHz and 5GHz in Europe too. Not to be confused with 2g (generation) and 5g mobile/cellular bands.