According to the product page:
"The ADI-2 FS also uses the conversion technology of the ADI-2 Pro: the AK557x family and the AK4490 not only offer 192 kHz sampling frequency and lowest distortion, but also a dynamic range of 120 dBA."
So, the ADI-2 FS seems to have the same AD/DA converter built-in like the older model ADI-2 Pro FS.
But not the same as the newest model ADI-2 Pro FS R BE, which uses e.g. more recent converter for D/A: AK4493
(sorry, A/D is not being mentioned here.
I propose you compare technical data from the manual, if this is of importance for you.
Regarding sound, most likely no audible difference. Transparent conversion, no mojo/house sound.
There is one important difference regarding ADI-2 FS vs. all other ADI-2 Pro products:
ADI-2 FS supports "analog loop-through" without AD/DA conversion between Analog IN and OUT, in this case only for monitoring, D/A conversion is being used.
Due to the design of the ADI-2 Pro, you always have an AD and DA conversion when routing from analog to analog.
Regarding ADI-2 FS, maybe also worth to be "highlighted", unlike ADI-2 DAC/Pro it has no USB.
Also no AD/DA filter, auto-reflevel and other ADI-2 DAC/Pro specific features.
See manual chapter 9:
https://www.rme-audio.de/downloads/adi2fs_d.pdf
https://www.rme-audio.de/downloads/adi2fs_e.pdf
Here are the manual links of the other products, if you want to compare technical data and do the Excel job:
https://www.rme-audio.de/downloads/adi2dacr_d.pdf
https://www.rme-audio.de/downloads/adi2dacr_e.pdf
https://www.rme-audio.de/downloads/adi2profsr_d.pdf
https://www.rme-audio.de/downloads/adi2profsr_e.pdf
https://www.rme-audio.de/downloads/adi24pro_d.pdf
https://www.rme-audio.de/downloads/adi24pro_e.pdf
BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub13