hey, thanks for asking about it, the final Asura has been done for a while, we were only holding it back as we found some minor issue with the production that we need to make sure, the beta Asura is a very good earbud also, but it can not handle big amps , and I don't think it is a good idea to sell them because of that.
As for the difference, the retail Asura will sound more like Zen, but can sound good with pretty much everything( from iphone to big "brick" DAPs / Amps), and the best part is they can take as much as abuse as Zen , which for us is very important.
I studied in Japan for my bachelor degree, and the Japanese customer services (especially , Apple Japan ) are ridiculously good, that is what we wanna provide for our customers , which is" we will really take care of our customers". The current beta Asura while sounds pretty awesome, simply can not deliver this kind of exp if it can take all the beating and abuse people normally throw at a high Z can/earbud