Unfortunately I can't speak as to finalized firmware. Amanero is a third party vendor and while we obviously maintain good communication with them as we use their product in all of our dacs, we don't have direct control over their meeting of deadlines and they have missed them in the past. I can say real progress was made and DSD256 is working pretty stably in Linux now.
You can indeed use DoP in linux, but my understanding is if you are not in native, the full benefit of 8xDSD won't be realized.
I don't have instructions to give at this time. When there is a stable firmware we will probably make the update available through our techs for a nominal fee, but in the meantime I can't instruct people to open their dacs to manually short their amanero boards and re-flash them with "pretty stable" beta firmware versions.