Thanks for the tips, guys … ran a BNC cable from the HD621 to the DSP3100HC and everything is now tickety-boo.

Cheers

Office: MacMini + Roon -> MS600 -> AR LS-9 -> M60s (1993 vintage)
Home: [AppleTV -> HD621] + [Roon -> 218] -> G65 -> DSP5200HC + DSP5200s + DSP3200s
Being a JAFA in Auckland, New Zealand