Sure there are a lot of nice softsynths to use with the TeensieWI, but if you also wish to use it with hardware synths with DIN-5 MIDI input, you can't do that directly of course. The options are to either go via a computer and reroute the MIDI data, or to get a MIDI USB host converter. The first one is not very practical in many situations, and the latter can be expensive and still a bit bulky. For pro use, I'd probably go with the Kenton converter, but if you just built yourself a €40 wind controller, you probably don't want to spend €100 just to make it work with your hardware synths. Sure, you could just use a serial TX port on the Teensy to get the signal out, but that would require another cable going from the controller. Also, with a USB host converter, you can do this with any class compliant MIDI controller, so that's a plus. After some internet searches I found the USB host mini from Hobbytronics.co.uk. It converts USB data directly to serial data, so all you need to get a working MIDI converter is a 5V DC regulated power source and a MIDI jack with a couple of resistors. You can easily fit it in a small enclosure and make yourself a cheap (< €20) converter dongle. So that's my little tip of the day :)