Layering electro with software pads/synth patches

[NordinOz]

Hi brains trust,

Am a new Electro 6 owner. I want to use the Nord together with software for improved layering of pads and synth patches underneath the nord piano sound (specifically Sunday keys app for mainstage using iPad). I can't afford a stage for independant layering of patches unfortunately.

Is it better to get a keylargo mini mixer and plug both the nord and software into that, or just use an audio interface like focusright? It will run to a DI box and then FOH. Not sure what kit I need to get audio from both the nord and software simultaneously (while playing just the nord keys).

I'm quite a noob, so would love your tips and insights o how to rig this up!