Classic (legacy) Sony ES receivers

Sony’s ES receivers supported serious external control long before the modern network API existed — the custom-install External Control protocol, originally RS-232 and carried over TCP on network-era models (port 6001 on the DA series, 33335 on the ZA series).

Couch Amp speaks it natively:

• Automatic discovery — legacy units show up in the network scan with a LEGACY badge and their real model name
• Power on/off (enable network standby on the receiver to power on)
• Volume in dB, with mute
• Input switching across the DA-series source list, including HDMI inputs
• Zones — Main, Zone 2, and Zone 3

On a legacy receiver the app trims itself to the two pages that apply — the faceplate and settings — since the protocol has no sound-field, EQ, or tuner control.

Make sure Setup → Install Setup → External Control is On at the receiver.

Verified against a real STR-DA4600ES; see the full receiver list for the DA and ZA models that share the protocol.