Sometimes, multiple mono reverbs can be more useful than
pre-configured structures for stereo, 5.1, 6.1, etc. With the M4
algorithm, you get access to 4 discrete mono reverbs with 4 inputs
and 4 outputs in one engine.
Of course, you can use the M4 reverbs traditionally as multiple mono instances, where the effect has to end up in predictable places, but you could also combine some of them to cover arbitrary multi-channel configurations like 7, 10 or even 16 main channels with different settings, all within a single Reverb 6000.