Are you trying to access the music files directly attached via hard drive to the BDP-2? Roon uses a core system on your iMac. The music files stored on the computer’s NAS, or USB hard drive will be utilized by the BDP-2 as an endpoint. You should be able to select the BDP-2 in ROON under Settings>Audio. The BDP-2 has to be booted and “ON” for Roon to see it.
Verify that under the BDP-2 services tab, Roon Ready is selected.
BDP-2 Settings> Services.
Take at look at Ken Krutsch’s response a few posts down in the below link…