Difference in sound between copper and silver digital cables?

RE: ...

All you need is to have every send bit being received correctly

And there lies the problem !!!

My understanding is...

With SPDIF, Optical and USB there is no way to know IF the data stream RECEIVED is identical to the data stream SENT

Ethernet is different - data is sent in "packets" together with a CHECKSUM - if the CHECKSUM calculated from the packet received is not the same the checksum sent with the packet - then the packet is resent until it matches. 

So - if there are errors in the SPDIF, Optical or USB data stream - the erroneous values are NEVER detected and hence, "interpolated" by the DAC to a best approximation of what was sent.

So apply these "Approximations" to L and R channels and what will often result is a phase differences between the channels, which will alter the image, change dynamics and degrade the overall sound

So getting a GOOD SPDIF, Optical or USB cable actually DOES improve  sound quality.

Regards - Steve  

Some companies actually do measure the cables and the info and graphs are on the websites.What I have found is it doesn't matter how the cables measure if the components(most of them) are unable to send and recover a perfect signal.Trial and error with different cables until you find the one by'happy accident' that seems to counteract the errors and allow your system to sing.The perfect cable could be one buried in your junk box,an expensive boutique,or anything in between.

I tend to doubt that anyone measures or publishes cable performance. If it doesn’t make sense it’s not true.

@wig  How does the cable you made compare, head-to-head, with the Inakustik?

Williewonka, the first layers of ethernet don't have checksum and you still need a shitty cable to fail at the physical or data link layer.

Statistics on my server (current uptime 27 days) : 

Iface     MTU   RX-OK RX-ERR RX-DRP RX-OVR   TX-OK TX-ERR TX-DRP TX-OVR Flg
lo     65536 2420653     0     0 0     2420653     0     0     0 LRU
eth0   1500 95001512     0     0 0     122699833     0     0     0 BOPRU

It's probably a bit messy to read here, but you can see there are no TX or RX errors at interface level (eth0 is the physical interface, ignore the 'lo' interface, that's the loopback aka 127.0.0.1).
Anyway, no fails on +200 million packets (RX and TX combined) on a 1000baseT connected with a 5$ Cat5e cable (length 5m).

PS : USB has a hardware checksum test, but USB audio/video devices use isochronous communication to avoid latency (thus no hardware checksum for that).