Delta Sigma DACs

Thanks everyone, that pretty much confirms what I thought.  Now here's the rub: I have a Cambridge CXU that I bought to play my CDs, and to play any SACDs and HDCDs I might want to add to my collection.    It has an onboard DAC with 5 Wolfson WM8740 chips, which use the Delta-Sigma decoding scheme.  I use it only for 2 channel audio, and have it connected to the line inputs of my preamp.  It plays Redbook CDs fine, presumably through the Wolfson DAC (the user manual is hopelessly incomplete).  I had wondered how that worked, but georgehifi's response addresses it, and makes sense to me.

So, you would think that it would be a cinch for it decode SACD's, right?  WRONG!  I recently got my first hybrid SACD, and when I put it in the CXU... nothing.  No sound.  After several email exchanges with their tech folks, they said that I could only play it if I set the "SACD output format" to PCM.  That does give me sound, but I can't figure out if I'm listening to the Redbook version or the DSD version on the hybrid disk.  Why on earth would they require me to use the PCM setting to play a SACD disc through a Delta-Sigma DAC?  Am I missing something here?

I’m afraid you’re stuck with Redbook layer. Your Cambridge CXU can output digital only as S/Pdif and this format won’t work for SACD.

I don't think that's correct; where did you read that?  The Cambridge site says it plays, among other things, SACD and HDCD formats: https://www.cambridgeaudio.com/usa/en/products/cx/cxu

If it was only capable of S/Pdif, how could it play SACD disks? 

Thanks @angelwars, I appreciate the additional info, especially since I thought this post had died. Since the last post (before yours) I picked up an old Benchmark DAC (version 1), which made a real improvement in the CXU’s sound with both PCM and DSD discs, but still doesn’t sound quite as good as my limited collection of SACD’s. Have you used any external DACs with yours?

@angelwars  I send the CXU Digital Coaxial Output to the Benchmark Coaxial Input, then use the RCA outputs from the Benchmark to my preamp. 

That's true -- I don't know why, but the CXU only allows me to send DSD via HDMI, and not by Digital Coax.  If I could take the DSD stream from the HDMI output of the CXU, and convert it to coax, I suppose I could feed that into the Benchmark and see how it sounds (not sure if that's possible; does anyone know?).  It's not a big deal, though, because the CXU's DAC does a nice job on my SACD's, so I can just send the analog output from the CXU to my preamp.