My 2 cents.
Android is a complex world: so many devices, so many official and custom roms, so many kernels...
I think it would be really helpful to know what are the minimum hardware and software requirement that make a device compatible with the dac.
Yes: there is also an hardware problem or is only a software problem?
Many people about the USB OTG feature talk about that a specific Android distribution and/or a specific kernel is not enough because many devices don't supply energy via USB.
In this thread James said that E18 works with the internal battery, so my question is: perhaps this means that there are no impediments from the hardware side for ANY device?
The software side.
My dream is a "universal" patch that can be make many device compatible with the DAC, but I know that is impossible.
The sad point is also that root and flash a custom rom or kernel is not something to everyone.
It would be really useful detailed guides for the various devices, as they are tested.
Finally, I would ask James (if are reading) to upload soon the official manual on the download page of Fiio site (there will be also ASIO drivers for use with the PC?).