To crossfade / blend between layers or keygroups use bi-directional Macros, so turning the Macro-knob to the left will shift balance to Layer 1 and turning it to the right will shift the balance to Layer 2 (use negative modulation values for one of the layers and assign the Macro to layer volume).
At  center position both layers play equally loud. Each layer can contain totally different oscillators / sounds / samples / whatever, of course you can also use LFOs or other modulators to perform the crossfading.

This way you can create interesting timbral transitions and pseudo-morphing effects.