imho you're a bit too optimistic regarding digital transfer packet loss.
You certainly know the effect of mismatched S/PDIF cables as you adress it yourself.
That could happen anywhere in the transmission path which I'd even extend right into the CPU. I don't trust the 'it's all numbers anyway' paradigm at all.
Myself using 2 different hardware DSP systems, and both deliver audibly 'superior' processing compared to Intel native stuff (didn't check G4 PPC yet).
I'm not biased in this domain because there was no need to add Pro Tools TDM to my rig.
But it just sounded (!) convincing and worth keeping - opposed to a lot of Intel VST stuff I tried and trashed over the years.
My suspect is based on the fact that a DSP card (regardless which brand) does synced stream processing that can't be interupted from outside. The OS/CPU has no access.
But even in this 'sandbox' complex processing may occasionally shift a bit here or there.
I know it because one of my systems allows to grab and check data at arbitrary points of processing.
I don't even want imagine how a multi-threaded desktop CPU will handle such stuff...
You may assume it performs flawless, because it doesn't throw an error and it's zeroes and ones anyway, but you just cannot be shure.
That's practically what happens on a digital cable when packets get lost. The stream may shift a bit here or there and it may add up.
But of course cable quality isn't related to gold plated hyper copper dunnowhat