If you want to do digital either opitical or coax will work out of it. I prefer coax as it can support upto 24/192 whereas optical limits to 24/96 and there’s something about an coax digital cable that feels more solid but that last bit is probably in my head.
I use this cable for CDs and streamer and really like it.
The DIGI-COUPLER 75 Ohm is our top level SPDIF digital audio interconnect cable, though is equally suited for Video and HF signal transport at a maximum performance level.
www.vandenhul.com
If your fancy ARCAM has a DAC it’s likely better than what’s in the bluesound so I’d connect to it using coax (there’s also the option to try it both using its own DAC with RCA and the ARCAM one with coax and deciding what you prefer).
If your ARCAM doesn’t have a DAC I’d probably not get both it and a DAC off the bat because cost.