I am setting up a system consisting of a 818 and two DSP5500s using an AC12. I connected a SpeakerLink cable to the AC12, an M5 cable to the left DSP5500 (set as Master), and an S5 cable to the right speaker (set as Slave).

In the configuration program, the 818 is set up with "DSP5200 (SpeakerLink)" and the left speaker as Master.

However, I only get sound from the Master speaker; the Slave speaker does not respond. I tried swapping them—setting the right speaker to
Master on the speaker and in the config program—and then sound came only from the right speaker, but still nothing from the left.

Interestingly, when I accidentally set both to Master, I got sound from both speakers and could control the volume on both.

I have swapped cables and double-checked all connections. I have also tried both "Type 1" and "Type 6" configurations with the same result.

What could be wrong?

TV room: 861v8, UHD722,Front 2xDSP7200SE, DSP7200HCSE, Side DSP5200, Rear DSP33, DSW, Velodyne DD 15 Sub,
Roon Rock NUC, QNAP NAS, Chromecast Ultra, Apple TV, Cambridge Audio 752BD, Pro-ject Pre box S2 digital, Philips Pronto remotes, Supra LoRad Power.
Office: 800v3, MS200, DSP3100
Basement: MS600, 502, 557, Dynaudio 52se, Dynaudio Sub 250