"Reality" is something sadly missing from most discussions about audio equipment.
I have had an interest in 'hi fi', sound repro and recording for over 50 years. When son and I became interested in computer audio we began as many do with a 'semi pro' sound card, the M-A 2496, first through a Behringer X802 mixer and later an Allen and Heath. Next was a USB interface, M-A Fast track pro. Over the next ten years we had a variety of interfaces, Berry BCA2000, Focusrite 8i6. Latterly a Native Instruments KA6 and now a MOTU M4. OK, none of those AIs is hyper expensive gear (although the M4 spec is pretty close to state of art) but we never found any difference in the SOUND quality of those devices. Surely, over more than ten years development you would expect some sonic improvements? But no. The ancient Fast track pro was very clean (mic pre were a bit ****) and yes, the M4 better but not audibly so.
Look also at the continuing interest in tape recording and vinyl? Tape produces noise and distortion many magnitudes higher than any of the interfaces mentioned above and so...LOGICALLY you would expect anyone hearing super clean digital sound for the first time to shun tape forever? They don't and, IMHO it is NOT because of some airy-fairy ideas about "harmonics"* but the fact that for MANY applications, well produce tape recordings are 'good enough'.
Bottom line: we are not 'bothered' by tape or MP3 which is 100 times or more worse than basic digital sound so why would we be able to tell the difference between two digital 'systems' one of which was only 'twice' as good as the other? People's ability to resolve sound 'quality' varies. guys like Hugh and James have innate ability but it has been honed by training and years of experience. Listen to them!
*In any case the main harmonic in tape sound is third, not second which is often said to be the "nice" one!
Dave.