You can add one and more rack mixers to your network and use their additional inputs, but you can not add more inputs/channels to your network. A SL 32 is a 32-channel mixer and will never be more than a 32-channel mixer. The only option is to use the network returns (Aux In 1, Aux In 2, Tape In) as "busses" for the added mixers, so the mix (Main L/R) of rack mixer 1 could be routed to Aux In 1, the mix of rack mixer 2 to Aux In 2. A third mixer could be routed to Tape In.
This can be a solution for "input groups" like choir, orchestra, brass or percussion. Using the AVB network for "adding" mixers instead of conventional connections (cables) makes sense, because you stay in the digital domain and can add Fat Channel and effects to the audio streams. Recording is also possible, if you can get along with 32+2 tracks.