I was an original investor in a kickstarter called the Prometheus System. After several slips on delivery, I complained and was given my investment back. So I decided to "Do it Myself". The approach is to have two extruders and only one hot end. The extruders are Bowden style and both feed a "Y" device that allows both filaments into the hot end, but only one at a time. This idea has been around for a while and there are several designs on the internet for making this "Y". I down loaded three and printed them and then designed my own based on what I had learned. So now I have to calibrate my two new extruders and then give it a go. Pictured below are the 5:1 geared all metal extruders, the Y and the Y holder that clamps to the top of the hot end.