Do I need an expensive digital cable?

It depends on the connection format!

For HDMI/IIS - very much; the clock is carried from the source to the destination. Any jitter induced in the cable, or noise injected, will affect the sound.  IMHO this makes IIS often a bad choice, unless it is superbly implemented and the cable is of the very highest quality.

For Coax & AES/EBU - perhaps; it depends on how good the isolation and re-clocking of the target are; if they are of the highest quality, then any reasonable, 75 Ω (110 Ω XLR for AES/EBU), cable - with the correct connectors, will work well.  If the target (DAC) is less well engineered you will hear a difference.

In the "old days" (1990's) Coax cable quality was critical as the clock was in effect reconstituted from the data bits and when they arrived; so jitter & noise in the input would affect the output.

For USB - probably not, if your target component (DAC) has implemented its buffering and clock properly, and if the USB receiver's isolation from noise was done well, SQ is probably unaffected by the USB Cable provided it can carry the signal reliably.

The better the DAC the more the output is sensitive to the the musical data content of the input but, paradoxically, the less sensitive it is to spuriae (noise, jitter) in the stream; and so is less sensitive to USB cable changes.

Bits are just bits - BUT (as in comedy) timing is everything and noise can ruin the performance - modern high quality DACs go to extreme lengths to provide stable clocks and isolate the analog output from noise in the input stream.

Forget Toslink except to hook up your TV perhaps, but then buy a good one.

ATT glass was the interconnect but has disappeared for connections to DACs.

In your case if your CD transport has USB output do use that, otherwise $150 should suffice (Kimber, Cardas etc. - look at the Cable Company e.g.).  30 years ago I would have been preaching very differently.

If we are looking at all aspects of the digital cable world then Clock Cables are critical.  Like coax cables in days of yore and IIS cables today they carry clock (hence timing) signals. They must not induce jitter and must reject noise. I am currently in the market for an upgrade here.

 @audio-b-dog

I also have the Simaudio 280 D with a Project RS2 T transport. I have used an optical cable, and currently using a DH Labs AES/EBU. Looking forward to your findings. FWIW CD sounds better than streaming.

I just received the "expensive" Purist Genesis Luminist cable. I'm beginning my test with Sade's "Love Deluxe." Wide, mellow sound with some underlying bass, cymbals, and of course i can't forget Sade's warm, smoky contralto voice. 

It might need a little bit to settle into your system even if it’s already broken in, and if it’s directional make sure you’ve got it installed the right way.  I installed mine backwards once and it was not good until I figured out my mistake.  Look forward to your thoughts. 

Okay, right off the bat, the digital cable is tighter. The RCA interconnect has a "smeared" sound which I found pleasant before I heard the digital cable. It's like writing in sharpie versus writing in pen. The Purist Genesis Luminist is tighter. I've just been listening to one cut, so I'll play it for hours on end, but I don't think the comparison will change. It wasn't a small difference. I heard it immediately when I plugged the "expensive" ($249 new) cable in. Now, is that just 75 ohm versus 50 ohm cables. My $14 75 ohm digital cable will be coming Wednesday. And yes, the cable is directional and I put it in the right way, even though chatgbt told me that directional is just a "marketing" thing.