How crucial is the quality of a digital cable?

Yes, a good digital cable matters, IMO. For quite a while I used a Blue Jeans from my CD player to my DAC, as I just couldn’t think it mattered too much, as it was….digital. I finally replaced it with a Silnote, purchased right here through AGone. Yes, more than $100, but it took all the glare out of my digital stream when installed, and much more ‘musical’. The Blue Jeans sounded ‘gritty’ in comparison. Much happier.

If you are going to do it, open up the wallet a a bit and get a good cable. I didn’t spend a fortune on the Silnote, but enough to make a significant difference. Just be aware, a digital cable, or any cable, can be too ‘soft’ or can be too ‘transparent’ depending on your rig, so understand which direction you want to go.

Taking the focus off the cable for a minute- when you use Bluetooth to stream from the amp what are you streaming to?

My experience with digital cables is very limited, so I'll give you my specific situation:

Bluesound Node ($600) connected to Maverick Audio Tube Magic D2 DAC with Sparkos Labs op amps ($400) with a digital cable.

First cable was a Blue Jeans Cable Silver-Plated digital coax ($30).

Second cable was an Audioquest Cinnamon digital coax ($100).

I did not hear any difference with this change in my system.

For reference, I have heard a difference with some power cables in my systems and with changes from Blue Jeans Cable LC-1 interconnects to Audioquest Chicago interconnects to Audioquest Sydney interconnections.

The reason that I purchased the Cinnamon digital cable was a direct result of my positive experience with power cable and then analog interconnect upgrades.

I have a new-to-me Denafrips Ares ii DAC that I am currently the Cinnamon cable to connect to the Bluesound Node.  I have ordered a budget USB cable to see if I hear any difference with a different cable/interface.

I won't say that digital cables cannot make a difference, but the mechanism for a difference being expected is much more challenging to identify.  I'm actually fairly happy that the audiophile rabbit hole seems to have a bottom in at least one area with my system.

I had excellent results from a Waudio power cable that was available for under $50 on Amazon.  It really improved things when connected to my Pathos Classic One Mkiii, but I didn't hear any difference on my other components.

I'll be surprised if a change in digital cables makes any difference for you, but I'll be shocked if it made a difference that was more significant than the difference you're hearing between your CD players DAC and your amps internal DAC.

Digital coax cables do make a difference. I’ve owned about 6 or 7, finally achieving the synergy I was looking for. It’s not just 0’s and 1’s. It’s the internal design and construction of the cable to keep the signal moving in a pathway without reflections inside the cable. Also the 75ohm impedance needs to match the impedance of the source output and input to the dac.

1.5 meter length is often the optimal length for the coax. And high cost doesn't mean higher quality.