Do I need an expensive digital cable?

@audphile1 

My 4 door sedan is capable of reaching a speed of 155mph. But it will perform much worse than a new porsche 911 turbo S at that speed

Ah, those Porsche rear-engined excitement machines. They have been called a triumph of development over design!  And why does Porsche label some all-electric models as Turbo S when there's not a turbo in sight?  But I do rather lust over one 4-door sedan whose price in Australia (A$300k) is on a collision course with its top speed (300-kph) - the Porsche Panamera.  On my desk, is a model of Porsche's electric 4-door sedan, the Taycan.

For a different explanation of why I prefer my DSD native, consider a humble Jeep. During WW2 some were fitted to run on rails and be used as locomotives. In Australia at least, dual system Jeep equivalents have both rail and road wheels and can run natively on either.

If I had to get from A to B where A and B are joined by an iron road, I'd be pretty miffed if the rail wheels had been disabled and my vehicle had to hop from sleeper (tie) to sleeper using the road rubber.

@rbstehno 

The better sounding transports use i2s to the preamp

You have picked the one digital link where the cable should really matter. I2S was never designed to be transmitted over a cable.

As a workaround, often an HDMI connection is drafted in for use by I2S, on the proviso that the cable length be kept as short as possible, under say 0.5m.

Digital works repeatedly and reliably because errors in transmission can be detected and corrected if decent protocols are used.  I2S by design does neither.

"Can anyone make a case that I should buy a "better" coax cable?"

Terms like better and expensive really don't mean much in this context, but I understand what you're asking. You can get a cable that sounds different than the one you currently have, but you have to be the one that makes the call on better sound. I found this in one of your other responses. 

"I was in the computer industry for years and even though I was in sales, I had to take a number of classes on various aspects of computing. Networking was one of them. I think that networking is done in packets. The transport sends a digital signal from its "digital out" optical and SPDIF cables. It sends an analogue signal through its RCA interconnects. Two different kinds of signals. "

A transport doesn't really send out a digital signal. It's actually an analog representation of the digital signal. Because of that, the signal can be affected by the same things that effects other types of analog signals in your audio system. Your last 2 sentences are confusing. It sounds like you may already know exactly what I just said, or do you mean the analog signal that comes out of a DAC? Most CD players can be used as a DAC or transport, that's why I'm asking. 

Either way, yes, a new cable can make a difference. However, you never really know what the difference will be, if any, so I would always try a new cable first. If you can, try more than one because they all sound different.  

@052rc 

My CD player has a digital out capacity with optical and coax. I assume good old Steve McCormack anticipated that DACs would get better and the UDP-1 owner might choose to run it through a newer more sophicticated DAC. The CD player sends out a 44.1 kHz signal, standard Red Book CD. What networking protocol I have no idea, though. 

The McCormack UDP-1 also has analogue out, of course. I use that, too, because it's a multi-disc player and my Moon 280D will not recognize SACD or DVDA or any higher resolution signal unless it comes from Qobuz, Tidal, or another streaming app. I send the analogue out signal directly  to my preamp and I can play my SACDs and DVDAs through analogue out.

@052rc 

A transport doesn't really send out a digital signal. It's actually an analog representation of the digital signal. Because of that, the signal can be affected by the same things that effects other types of analog signals in your audio system

That is disingenuous.  It leaves out what makes digital special compared with analogue, namely the ability to 'square off" the analogue and to treat the result as an integer number.  Numbers can have error detection added, and protocols can correct errors.  Redbook CDs can correct 4,000 consecutive bit errors.  That's why no matter how often you copy a digital file, you either get an exact replica or an error.  Degraded digital signals don't sound at all like analogue distortions.  If you don't like the sound, and describe the changes in analogue terms, something is getting into the analogue part of your playback chain.

Or you have a digital link which is not error corrected, or simply drops information. That's the original meaning of streaming.