There is another way to get stereo from an ios device without 11.3 and homepod update.
It has been known for quite a while now that with a mac you can set up stereo homepods with airfoil.
First set up Airfoil
1. Download AirFoil
from Rogue Amoeba’s website. AirFoil is a paid application at $29 per user.
2. Once you have AirFoil downloaded, copy it to your Application folder.
3. Open it and ensure that all of your AirPlay-enabled devices appear.
4. Choose your audio source. Easiest way is to choose System Audio. Then all sounds from the mac will play. But if you are a bit fussy about mouse clicks not coming through for example you can select specific apps instead which will exclude such noises.
5. Go to your Applications folder on macOS and find the AirFoil app. Right click on that file and choose “Duplicate.” This makes another copy of Airfoil called Airfoil copy.
6. Open Airfoil copy. It will open right over the Airfoil window. Move it away from it.
7. In AirFoil, choose the HomePod that’s on the right side of your configuration. Click the equalizer icon along the top and drag the “Balance” slider all the way to the right side. This will play only the right channel through that HomePod.
8. In AirFoil copy, choose the HomePod that’s on the left side of your configuration. Click the equalizer icon along the top and drag the “Balance” slider all the way to the left side. This will play only the left channel through that HomePod.