For straight-up audio production i9 is overkill (unless you're working massive projects).
If you're a hard-core composer... running massive orchestral templates, you want an i9 based machine.
 
Is the 8086k worth the difference in cost?
To me, that's easily... yes.
Over the life of the machine, the small difference in cost is nothing.
 
With the 8086k, you can run all six cores locked at 5GHz... and (with the right cooler) it's near dead-silent.
I recently started using a Presonus Quantum... so I could run Helix Native at 1ms total round-trip latency.
That's a heavy load on the CPU... and I want every speed advantage I can get.
This is a much different scenario than a typical general-purpose user.