How is your system set up? If your WiiM’s line out is set to an input on a powered speaker, yes, you’re out of luck once you want to airplay the line-in on the WiiM to another speaker.
However, if you are using a receiver that has an Auxiliary in (input only) and a set of Tape In RCA connections: Record Out and Line In, you can: play music on the amp through the Aux RCAs, but pipe the Record Out to the Line-in on the WiiM. You can send that audio to any of your other speakers over airplay.
I wouldn’t use the Rec Out and Tape In because you could end up with a nasty feedback loop if you select the Tape input. Feedback was a problem you had to avoid if you wanted to monitor a tape recording on a three-head deck.
Record Out is like a pre-amp out, but at line-level. It will output all music coming from any other components you have hooked up to the inputs on the amp. So, if you’ve got a record player, digital disc player, tape deck, etc., you can play that audio to other WiiM or Airplay targets.
The only issue would be that the music played to other speakers will be delayed compared to what is playing on the receiver that is hooked up to the line-in on the WiiM.