So I'm watching Youtube videos of how to use the Yammie YAPAO speaker adjustment feature. Well. I saw a vid on using a sound pressure meter to adjust individual speaker volumes.
I purchased one but BEFORE i used it I adjusted the volumes of each speaker using the YAMMIE software [Yammie "Settings" on the remote].
After my adjustments, I turned on the sound pressure meter and guess what? The meter told me that I had adjusted all the speakers correctly.
So you may not need a $38 SPM. But its a cheap toll in my box.