Please read carefully this thread to find out that, with well implemented devices like DX200, conversion to DSD lower than DSD512 has no sense, and why it is so (in brief: because a good DAC does it anyway). Then, I doubt that Fiio has implemented on-the-fly conversion to DSD512 or higher
I believe you are right, and despite the FP performance of A73, it is still a question mark for me how they could achieve on-the-fly conversion (and the quality of their algorithms). Maybe with looong buffering, maxing the clock and dropping the battery life to 1 hour while radiating heat enough for frying an egg. Still I find it pretty interesting that they attempt to do it. Let's wait and see what will come out.