Android 13 car head unit won't route phone calls or AV-IN audio to USB DAC/AMP

I have a full blown Android 13 car head unit - EX-ALS215 (Snapdragon 662). Audio is output from a 3.5mm jack socket on the unit's harness (audio-out socket). I have then connected a Cyrus Soundkey DAC/AMP to one of the USB sockets of the head unit. All audio is now output via the DAC except phone calls and the audio from the AV-IN. (AV-IN is part of the unit's harness and is where I plug my TV tuner as input [Video/L/R]) So, voice calls and AV-IN persist in coming out of the 'audio-out' socket on the harness. **Why is this happening and how can all audio be routed to USB?** **Clue#1:** I have tested the Cyrus Soundkey with a Samsung Galaxy A53 and when making a phone call the audio from the call was correctly routed to the earphones plugged into the DAC. The microphone used during the call was the one built into the A53. I am at a loss as to what is happening. **UPDATE#1 (01 Feb 2024):** I used adb to investigate why this is happening. Can you see anything obvious in the text files? or Would you like me to try something else? **OBSERVATIONS:** 1. I am no expert, but is dumpsys audio showing the "Cyrus Soundkey" (usb_headset(4000000)) being the default for voice calls? post.com/forums/attachment.php?attachmentid=3377686&d=1706801391 2. dumpsys media_session : shows the com.wits.ksw.bt application (the KSW BT dialer) making a voice call? Does this mean that kswBt tries to output to the Soundkey and it fails, defaulting back to the builtin speakerphone (as seen in practice)? **UPDATE:** This entry does NOT represent a phone call. Instead it represents BT audio played on my phone via this BT app which is also responsible for voice calls. Indeed BT audio from my phone played using this app, does go through the USB DAC. **SUGGESTIONS:** 1. Is it possible that the Soundkey is being rejected due to an audio incompatibility with the telephony audio (24bit vs 16bit or something)? 2. Someone suggested that A FiiO Q3 DAC would work with voice calls because it supports USB Audio Class 1.0. Others have said that a FiiO K3 DAC which also supports USB Audio Class 1.0 exhibited the same problem with voice calls. (FYI. The former has a unit from same manufacturer as mine, bought 2 years ago and upgraded to A13 & current firmware. The latter was from same manufacturer in 2020 A10.) **LINKS TO FILES:** dumpsys audio , media.audio_policy , dumpsys media_session , media.audio_flinger .