I can confirm that my DSP7200s work with an HD621. Selecting an active source will switch the HD621 to the correct input.

The left speaker is set to Master and Controller.

The HD621 is connected for comms using a BNC to BNC cable to the BNC comms input (and yes I do mean input*) on the left speaker.

The left speaker is connected to the right speaker using Speakerlink.

BUT I have not got it working for sound (yet) because of laptop issues. So it is still on an old 6-channel config.

The config is (relevant settings only) as follows:

Setup
- System Address = 1
Audio (down column)
- Smartlink/MMHR, Smartlink, 6 Ch, Yes, Yes, Yes, Yes, Yes
Types
- unknown (see my previous posts above) - but probably = 0
Connections
- C = Meridian Comms Input


* Just physically/visually checked as I realised I had taken out a G68 (which had been the Controller)