You can play music on different players by simply open new tab on the browser then select the player from the LMS web-interface, you can open many tabs and select many players, but make sure that squeezelite service is running first, so you can see the player on the LMS.
I figured out by trying.
You fist have to choose the right „mode“ on the IQAudio page.
After choosing the Multiroom setup – everything was fine and the server showed up the player 😉
It is good to know that your problem has been solved, Multiroom setup is the best solution for your setup beside the solution that I suggested before .