Regarding “damaged” Bits:
Bits are transferred as changes between two defined voltages, e.g. like +0.4V for Hi and +0.1V for Low.
To do this, a cable’s capacitance must be charged and discharged back and forth, which takes some time for each Bit, the more the longer a cable is.
Imagine a transfer path like an SPDIF coax cable that’s just slightly too long.
Now most of the time each Bit change between Hi to Low, just so, reaches the trigger voltages before the next Bit is to be send.
From time to time, due to noise e.g., this does not happen, a bit change is lost, the Bit “hangs” or is “twisted”, basically the same thing.
This degrades signal quality, or results in audible clicks.
Practically most data on external cables or through the air aren’t sent as single Bits, but as packets with some error correction, often even with the option to re-send defective packets.
But for SPDIF Optical and Coax, and AES digital this is not the case - what’s lost is lost and causes signal degradation.
To have a simple tool - RME BitTest - to detect this (and other less significant signal changes) is a great achievement.
To my knowledge no other DAC offers this.