Native DSD playback for iFi stuff has been in the kernel for some time, since the mainline 3.19 kernel. The reason iDAC2 doesn’t ping when searching for information on this (other than it not being as well known/popular) is the fact it was not yet released when the patches were introduced. At any rate, they (it and the Micro iDSD) use the same unified firmware.
No problems with native DSD playback here on my iDAC2 / Arch Linux Alarm based NAA. In fact I don’t even have the firmware installed that would allow 256 over DoP.