Just wanted to add, I decided to get back into some visual design again. I definitely would not count out Unity3D, especially with its new GPU based Visual Effects Graph.
Very easy to implement Ableton link to sync timing, much support for midi/osc etc. Screenshot is of my latest project, simple VFX graph usage with link implemented.
As for FFT monitoring of live audio, not really too feasible, but you could also just split some channels in daw (low/mid/hi) and do some midi/osc conversion with some type of volume rider plugin. Send that to unity instead of needing to monitor audio and all good.