Velleman K8062 DIY kit is one of the most successful DMX transmitters sold world-wide, but it is also one of the poorest performers. Velleman uses an antiquated slow speed USB protocol on a device that supports Full Speed USB.
A community developed firmware upgrade that offers up to 80x times better performance is currently undergoing beta testing. It supports Full Speed USB and is developed alongside drives for multiform use.
Via the forum.