Thanks @B00t-eek!
Looks impressive, but is not (pin-)compatible with the audio board 
(at least not without an adapter board). Also it seems that not everything from the audio-lib is currently supported.
Regards, Holger
I am in when you are going to make your project compatible.
I think I’ll wait some days/weeks until it’s “more stable”… But it looks like it has enough power for massive Dexed AND MDA-EP in one uC 
teensy are fantastic. they have MIDI and Midi Usb (x4) firmware support, so you can make a midicontroller and send midi messages from the usb port.
Update and new information for the Teensy-Audio-Board and Teensy-4.0: https://www.pjrc.com/store/teensy3_audio.html
… and some more information about a breakout board for the Teensy-4.0 and the audio card (no DIN MIDI):
… and some more information about a breakout board for the Teensy-4.0 and the audio card (no DIN MIDI):
https://www.pjrc.com/breakout-board-for-teensy-4-0/
Update - new model… https://www.pjrc.com/teensy-4-1-released/ More I/O, SD holder.
Two I2S means could have multiple audio cards… might be a good low end, single instrument host. 
Apparently overclockable…
I ordered one for testing with MicroDexed. It seems to be (pin-)compatible for this usage.
Thanks for showing!
Soldering on memory upgrades. Finally a return to the most exciting adventure of 1985!
My first memory upgrade was solder free - from 4k bytes to 8!
Compukit UK-101 ,MS Basic, 6502 at 1mHz, 1982!
It used 3 Amps at 5 volts.
I did solder a cassette speed doubling switch (300 baud to 600), and via AY-8910 PSG soundboard port, a Wasp synth was sequenced.
Good news: Works with the encoders and LCD display inside MicroDexed when replacing the T_3.6 with the T_4.1
Bad news: Teensy audio shield Rev B and C are (currently?) not recognized (and also not the SD slot on the audio shield). I asked for a software solution in the PJRC-forum.
yeah teensy 4.1 needs rev D audio board
rev c needs some wire changes