Two Sources, One DAC

The Bluesound Node 2i has optical and digital coax output options.  I don't think it outputs USB.

I think the digital coax (SPDIF) is considered to be superior so use that for your primary or superior source.  If you have any high resolution files then they will only work over SPDIF so that could make the decision for you.  I would guess your SACD player outputs redbook via digital outputs and SACD only via analog.

Your Denon will probably only have COAX and Toslink digital outputs as does your Node so they will both be fighting for the same COAX input on the DAC unless the Denon has aes/ebu out or you can find a DAC that takes two COAX inputs. Forget Toslink. The Denon will play SACD through it's digital outputs but it'll be DSD over PCM (DoP) not native DSD, but it's a good idea to get a DAC with DSD capabilities because it'll allow you to upsample to DSD which you may like and use DSD in the future.