Series III Consoles and Rackmixers have a max input channel count of 32 channels plus a few Stereo return channels. (with the exception of the StudioLive 16R and 64S.)
Adding an additional mixer via AVB will allow you to have more Input sources to choose from, however, the main mixer that is USB Connected to the computer will still only support up to 32 inputs at one time from the AVB network.
Channel count for each model is further shown here.
https://www.presonus.com/products/StudioLive-32R/compare-models
If you are using Apple Computers, you may be able to get more inputs using AVDECC and routing AVB with your Mac acting as a routable I/O point. However, this would not show both StudioLives as one mixer- they're control would remain separate.
https://support.presonus.com/hc/en-us/articles/360050823871-StudioLive-Series-III-Can-I-use-AVB-Network-Audio-with-my-computer-
