In case you are looking for an inexpensive and an easy-to-build MIDI THRU solution, Andy has built a new PCB for this job! :)
It is good for low-latency MIDI distribution, supports normal and TRS MIDI connectors and offers a visual MIDI traffic indication using a superflux LED. Also, it is multi-chainable to 8x MIDI DIN and 6x TRS MIDI or even more outputs. Using these boards, you can extend your SEQ MIDI OUTs to drive a lot of MIDI synthesizers with minimal latency! :-).
The USB port is intended for easy portable jamming setups, or you can alternatively power it via a pinheader.
We've also included a build photo tutorial. https://www.midiphy.com/en/shop-details/0/35/
Enjoy and many greets!
Peter