I wanted to change the default look of all icons on MIDI studio on my Mac, and I found an easy way to customize them:

I have modded a Melotone Toy Drum, with very simple mods:

• External power supply (solder wires to battery terminals)
• Speaker On/off Switch (solder wires from switch to speaker)
• Audio Out (take signal directly from speaker)
• Trigger ins for Eurorack (simply connect a Jack to th epins of the IC, follow traces from pads to IC)

Here's the result, triggered by my Beatstep Pro:

I recenlty found on eBay a "MUSIC 64" keyboard, with not many details, no warranty...I offered 10 euro to the seller and he agreed to sell it to me.
After some days I receined it, it was in pretty good shape and more imporant: it works!
I found some ROM images for its softwares (MONO64 and POLY64), here's a quick demo of the presets on the POLY64

You can edit various parametes of the synth enigne.

Upon request by a member of an Eurorack Facebook Group, here's a simple modification of the original Temps Utile Firmware, that adds another memory slot, bringing the available location for user presets to 5, but could be increased to any number apparently.
I haven't tested it thoroughly but it seems to work. 
DISCLAIMER: I take no responsibility for loss of important presets. use another Teensy if available, just in case...

Download it here