UD - what is the advantage of the L2 system, beside the speaker direction?

If I use the keyboard mixer and harmonizer, do I need anything different, like that mixer they offer?

zuki
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Yamaha 920 / Yamaha DGX-670 / Maui 5 Go (2) / Senn e935 / Sony C80 / Tascam DP24sd / ATEM Mini Pro switcher (studio)