I'm not sure "Pro" means AD/DA conversion. The ADI-2 FS for example has AD/DA conversion but isn't labelled Pro.
Pro seems to just mean onboard DSP, but only if the unit isn't labelled DAC. So ADI-2 DAC FS has DSP and ADI-2 Pro have DSP but ADI-2 FS doesn't have DSP.
The "R" isn't always used consistently, either. For example, the "ADI-2 DAC FS" has a remote but doesn't have the R (at least officially, though I've seen it referred to as the ADI-2 DAC FS R in some places, but it doesn't say "R" on the faceplate). I think R or the lack thereof is mostly only meaningful if PRO is present.
The other thing that causes confusion is that they stopped using version numbers on newer units, so there are two versions of the ADI-2 DAC FS out there that are hard to tell apart unless you plug them in and look at the menus or open them up.
Yes, I find the nomenclature very confusing.
There is ADI-2 FS which has AD/DA
an ADI-2 DAC FS which is DA only and no version number and the photo on the RME website shows the older version (no kensington lock) but has the new remote