Each Layer has an independent set of synthesis controls, and there are many parameters that will only affect the individual Layer. However, there are also a number of Common parameters that are shared by both Layers in a Part. Most of these Common Parameters are accessible from the Main Page.
If a parameter is numbered, then it’s a Common parameter that can be used by both Layers (ex: LFO 1 ~ 6, Mod Env. 1 ~ 4). If it isn’t numbered, then it’s specific to the Layer (ex: Amp Env., Filter Env.)
Common parameters include the six LFOs (LFO1 ~ LFO6), the Master Filter, and the four Modulation Envelopes (MOD 1 ~ MOD 4).
In addition, each Part has four FX Racks: a Common FX Rack, an Aux FX Rack, and an FX Rack for each Layer. For additional detail, refer to FX Architecture