couple of ideas:
Jon would you consider selling your tinybox design to someone like sound professionals, they might bite.
Also recently I priced out assembled boards from itead and shenzhen, and the assembly costs were not that bad, in volume it might work out for you. Plus they source all the parts from standard suppliers so you would not need to stock parts, order, etc.
I agree about the tinybox form factor, it was great.
(why was I inquiring about assembly? - stay tuned for the 6 channel altoids mixer)