Thank you for your quick and comprehensive answer.
As a matter for fact, my suggestion for an ADI-2-Network player was more generic than for the sole purpose of solving my specific needs which are slighty different frome the generic businessopportunity (NAS servers with remote DAC) that I described.
The solution that you suggest, as I understand it, is a point-to point Toslink connection between the file server and the DAC. It would certainly work, but it is not well adapted to my personal configuration that I describe below. More generally, a network player as I suggest it has the benefit of working on a LAN wich is more flexible than a point-to-point.
I currently have an old high-end Lyngdorf DAC/Processor/Active-filter/Balanced-preamp that I use only with digital sources : Blu-Ray, TV and a MacMini running Audirvana. The Lyngdorf has no USB input and I am using an optical connection from the MacMini, with an iFi Ipurifier Toslink/Toslink signal cleaning and recklocking device, that I plan to replace with a Mutec USB. I previously had a M2Tech USB to Pdif/RCA interface, but it did not work well with my recent MacMini which has a very very noisy USB interface.
Within a few monthes, I shall move to a new home where I plan to have 2 rooms for music : the living room where I plan to install my full configuration with the Lyngdorf preamp, and my "home office" where I plan to listen with headphones or desktop speakers or short-range monitors. This second room will require a new DAC, the RMI ADI2-DAC being my favourite candidate.
Since the electricity is going to be refurbished, I have asked for a ethernet LAN to be installed, but I do not believe it is possible to install a fiber link because of the weird cable pathway. I shall install the MacMini in the living room since unlink a NAS server, it has a silent SSD disk and no fan and connect it to the Lyngdorf. I will have a MacBook notebook in my "home office". Thus, the simplest solution would be to connect the DAC to the MacBook in the "office", and access the music files on the MacMini over the LAN. Unfortunately, this has several potential drawbacks :
1) It will not work when the MacBook is away, off or is not on the desktop.
2) The MacBook also has a noisy USB output. I am concerned that the USB noise will pollute the DAC sound. I don't know if RME has designed the USB input of the ADI-2 DAC in order to eliminate the noise. At least, since the USB input is asynchronous, it should not be affected by the USB jitter.
I could connect the MacBook in my "office" to the DAC with SPDIF/Toslink, but there would be no point anymore to buy a USB DAC. Furthermore, from my reading of the ADI2-DAC documentation, it does not use it's internal clock when connected to a SPDIF input and uses the input's clock. This significantly reduces the interest of the ADI2-DAC in such a configuration.
Thus, in my configuration, a network player connect to the LAN that would receive DLNA streams from the MacMini would be the best solution. And I believe there is a point for a generic product from ADI.
Thank you again for taking the time to answer.