I plan to do the same thing, I mean, I'm already doing it and have several early prototypes, but still not a full finished product, I want really high end finish on it before revealing it, meaning CNC machined aluminium, anodized and sandblasted, high quality mahagony wood pieces and 3d printed parts. I have 4 headphones designed at the moment fully, down to the last screw and padding material, and I must say (can't release yet) they also have some things not found on any headphone I'm aware of in terms of design. The issue is I also have about 1000 files of prototypes and parts done in autodesk inventor that I don't use, not that they're bad, in fact they're better than what most hi-end headphones on the market feature, it's just that I design something, it looks very good and then I decide to slightly change it without trying the first version, which leads to a painful situation in which the ideas are flowing out of my head like a water out of a fountain, but I can't build each idea into a real product, because prototyping is EXTREMELY expensive. Think of it like this....you can buy some HD800's for the price of having just the aluminium pieces machined and finished in small quantities. That problem is keeping me from going all out and finally building a headphone, I just can't decide which version to go with. I'll have to pull the trigger once I get the final drivers. I can't decide on which drivers to use at this point, I am torn between AKG K812 (around 300 dollars a pair), ATH-AD2000x or 1000x drivers (around 150 a pair), or go with something cheaper like the Ypsilon and try how that works out first. I'm pretty sure my build will be an open back headphone first as well, so the Ypsilon driver is just fine. Choosing an open version because they're more easily tuned and the positioning of the driver will be such that the open back design will be most beneficial for the soundstage and imaging, I already got my prototype to image and throw a deeper soundstage better than my Beyerdynamic T1's, and that was using the drivers out of a Superlux HD681 which cost 20 dollars and some very minor EQ-ing to fix then balance between both channels.