Way to go LinuxWorks! I have been a follower of your arduino projects for about 2 years now after that first head-fi post.
I have been out of the audio game for a while (at least for posting). It is great that you guys are offering up a Stepper, since the TPA Joshua Tree has been the only thing out for a while and yours seems to have more to interface to? Gotta love the Sigma22 PSU, it is such a beast!
BTW guys, the AMB boards are TOP NOTCH! I have built a few of his designs including the venerable Beta22.
In the furture it might be nice to offer up a GLCD LCDuino. I ended up not going with an LCDuino because I wanted it to make analog meters on the display as well as system information. The Topway LM12864LDW works pretty darn well and isn't too expensive, but it does use a lot of I/O (which is why the Mega might be a better choice).
Also, it would be pretty sweet to make a ATTINY based SMD Potentiometer w/ 64 steps. This would be a cheap volume controller for small portable amplifiers or MilletMax. You could probably fit it in the space of a normal Alps Blue spot and just put some Voltage and ISP headers on there for re-programming. Then give people the choice of using the mono cheapo potentiometer of their choice for control (including the little slider ones... want for my stamp-amp smd op-amp based about the size of a stamp 3.3v).
All the best and GREAT WORK!