Planning an audio synthesizer project

I'm working on a hardware synthesizer project (which will at some point scale up to mass production of 1-2000 units): the typical box with midi-input, audio output and a bunch of knobs and buttons and LEDs on the user interface.

Backstory: I've built my proof-of-concept around a Raspberry Pi, with an off-the-shelf USB MIDI controller and a USB DAC plugged into its USB ports. As I was investigating how to redesign the MIDI controller for my specific purposes I started looking into Teensy as one of the obvious candidates.

Now that I see there are some rather powerful Teensy variations (3.5 and 3.6) I'm wondering whether to move the entire project including the synthesis engine to the Teensy platform.

My main question is: not having experience with running processor-heavy applications on an MCU I have no idea how much performance I'd be able to squeeze out of the M4 compared to general purpose CPUs (like the A7 running a stripped Linux OS on top). Would the 180MHz clock speed be sufficient for simultaneous realtime audio synthesis at a serious quality level and MIDI handling - given proper code optimisation? I'm not afraid of doing SIMD assembler coding. Or is it wise to wait out until higher speed M7 boards become available or stick with CPUs rather MCUs instead? Secondary question: how feasible is it to turn the Teensy 3.x architecture into a custom production-ready PCB? I'd be working with a company providing industrial PCB designing expertise but I'd like to have a feel for the complexity. This would include integrating the audio DAC onto the PCB etc.

Thanks a lot for any insights.

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Why wouldn't you ask questions about the Teensy on the Teensy forum?