Each chain can have up to 32 I/O, 8 per algorithm x 4. So (in theory) you may use a whopping 128 channel inputs/outputs in total.
This is not a really useful scenario except for possibly some FOH tasks, but it would work.
IMHO using 32 channels is a very reasonable usage of the DSP power for a stereo (2.0) setup. You can use 16 algorithms with stereo input/output in parallel then – more than sufficient even for bigger setups. For 5.1, you would aim at 96 channels probably (if really all algorithms use 5.1; if not, 64 may well be sufficient).