Side comment: would be better to open a thread for your topic instead of randomly picking one to hijack it for your purpose.
Side comment 2: the products name is ADI-8 DS MK III, not ADI-8 DS MK III.

Converter quality is difficult to compare / rate. Generally spoken every converter works already on a quite high level and the analog circuit in front of an A/D and behind a D/A converter has also impact on the quality. Usually RME converter are known to work transparent, non colorizing the sound.

You should check this only on your own by performing valid listening tests at the same volume level and by excluding psychoacoustic effects by performing blind or double-blind tests.

You can take some data from the technical specification (see manual) to get a rough indication in terms of SNR/THD.
Or to check, how many / which reference levels are supported.

The ADI-2 DAC/Pro series of converters have additional features
— 4 reference levels
— auto ref level
— dynamic loudness (maybe not for studio use)
— different AD/DA filter, but this also results in only very subtle differences.

Other factors to consider:
— is your room optimized
— your personal hearing capabilities
— what equipment to connect, whether it has e.g., lower specs

Other things to consider, I/O ports
— what recording interface you have now
— whether you have enough ports, to connect e.g., an ADI-2 Pro

If you have UCX and ADI-8 DS MK III then the only one ADAT port is already in use for I/O.
The only possibility to connect an ADI-2 Pro is via SPDIF coax.
Possible, but my personal preference would be to connect it via ADAT or optical SPDIF to have galvanic isolation to completely exclude any potential hum that could perhaps arise.