How crucial is the quality of a digital cable?

I recently purchased a Cambridge Audio CX 81 integrated amp. The analog inputs sound great, but I find the internal DAC to be a disappointment. It uses the ESS Sabre ES9016K2M chip. I use a mid-level Rotel RCD 951 CD deck as a transport via the digital coax. I also hooked the deck via the analog out, just to compare. The analog interconnects are entry level AQ's. The digital coax is an Amazon purchase in the $15 range. I find the internal DAC of the 20 year old Rotel to be superior to the new AX 81, when doing an A/B.

What then confuses me is that the Blue Tooth streaming from the amp is quite good. It is HD aptX,  24-bit/84kHz capable. But, wouldn't that also go through the same internal DAC? Could it be the mediocre Amazon digital coax cable? I always assumed that digital cable quality was less significant than analog cables. Just bits and bites, right?

If someone knows of a decent digital coax for under $50, I would be very grateful. I would also appreciate any advice on an entry level power cord for the amp. Can a decent power cord be had for under $100? 



Mogami is always a safe and relatively affordable  bet for quality wires.  

I believe you've analyzed your problem correctly.  Quite sure a better coax cable should help but I don't think a $50 cable will do it.  Audioquest makes decent coax cables but you may need something like the Carbon.  If you order through someone like Amazon you can always return it if you don't hear a difference. I also recommend the Cardas coax (I use one) but you're talking alot more money, 

Get this.  It’s $55 for a 1m cable and you can just return it if it doesn’t make a meaningful improvement.  Just make sure u pay attention to the faint directional arrows as they are not just a suggestion.  I installed mine backwards once and it was a disaster.  Let it burn in for at least 100 hours and I think you’ll be pleased.  Best of luck.