I also have an Onkyo TX-NR626 connected to an Tanix TX6 with Allwinner H6. For me it works out of the box:
2022-01-02 15:42:11.156 T:691 WARNING <general>: Pulseaudio module module-allow-passthrough not loaded - opening PT devices might fail
2022-01-02 15:42:11.156 T:691 INFO <general>: Found 2 Lists of Devices
2022-01-02 15:42:11.156 T:691 INFO <general>: Enumerated ALSA devices:
2022-01-02 15:42:11.156 T:691 INFO <general>: Device 1
2022-01-02 15:42:11.156 T:691 INFO <general>: m_deviceName : default
2022-01-02 15:42:11.156 T:691 INFO <general>: m_displayName : Default (allwinner-hdmi 5091000.i2s-i2s-hifi i2s-hifi-0)
2022-01-02 15:42:11.156 T:691 INFO <general>: m_displayNameExtra:
2022-01-02 15:42:11.156 T:691 INFO <general>: m_deviceType : AE_DEVTYPE_PCM
2022-01-02 15:42:11.156 T:691 INFO <general>: m_channels : FL, FR, LFE, UNKNOWN1, FC, BC, BL, BR, BLOC, BROC, FLOC, FROC
2022-01-02 15:42:11.156 T:691 INFO <general>: m_sampleRates : 32000,44100,48000,88200,96000,176400,192000
2022-01-02 15:42:11.157 T:691 INFO <general>: m_dataFormats : AE_FMT_S24NE4,AE_FMT_S16NE,AE_FMT_S16LE
2022-01-02 15:42:11.157 T:691 INFO <general>: m_streamTypes : No passthrough capabilities
2022-01-02 15:42:11.157 T:691 INFO <general>: Device 2
2022-01-02 15:42:11.157 T:691 INFO <general>: m_deviceName : sysdefault:CARD=allwinnerhdmi
2022-01-02 15:42:11.157 T:691 INFO <general>: m_displayName : allwinner-hdmi
2022-01-02 15:42:11.157 T:691 INFO <general>: m_displayNameExtra: 5091000.i2s-i2s-hifi i2s-hifi-0
2022-01-02 15:42:11.157 T:691 INFO <general>: m_deviceType : AE_DEVTYPE_PCM
2022-01-02 15:42:11.157 T:691 INFO <general>: m_channels : FL, FR, LFE, UNKNOWN1, FC, BC, BL, BR, BLOC, BROC, FLOC, FROC
2022-01-02 15:42:11.157 T:691 INFO <general>: m_sampleRates : 32000,44100,48000,88200,96000,176400,192000
2022-01-02 15:42:11.157 T:691 INFO <general>: m_dataFormats : AE_FMT_S24NE4,AE_FMT_S16NE,AE_FMT_S16LE
2022-01-02 15:42:11.157 T:691 INFO <general>: m_streamTypes : No passthrough capabilities
2022-01-02 15:42:11.157 T:691 INFO <general>: Device 3
2022-01-02 15:42:11.157 T:691 INFO <general>: m_deviceName : hdmi:CARD=allwinnerhdmi,DEV=0
2022-01-02 15:42:11.157 T:691 INFO <general>: m_displayName : allwinner-hdmi
2022-01-02 15:42:11.157 T:691 INFO <general>: m_displayNameExtra: ONK TX-NR626 on HDMI
2022-01-02 15:42:11.157 T:691 INFO <general>: m_deviceType : AE_DEVTYPE_HDMI
2022-01-02 15:42:11.157 T:691 INFO <general>: m_channels : FL, FR, LFE, FC, BL, BR, BLOC, BROC
2022-01-02 15:42:11.157 T:691 INFO <general>: m_sampleRates : 32000,44100,48000,88200,96000,176400,192000
2022-01-02 15:42:11.157 T:691 INFO <general>: m_dataFormats : AE_FMT_RAW,AE_FMT_S24NE4,AE_FMT_S16NE,AE_FMT_S16LE,AE_FMT_RAW
2022-01-02 15:42:11.157 T:691 INFO <general>: m_streamTypes : STREAM_TYPE_AC3,STREAM_TYPE_DTSHD,STREAM_TYPE_DTSHD_MA,STREAM_TYPE_DTSHD_CORE,STREAM_TYPE_DTS_1024,STREAM_TYPE_DTS_2048,STREAM_TYPE_DTS_512,STREAM_TYPE_EAC3,STREAM_TYPE_TRUEHD
2022-01-02 15:42:11.157 T:691 INFO <general>: Enumerated PULSE devices:
2022-01-02 15:42:11.157 T:691 INFO <general>: Device 1
2022-01-02 15:42:11.157 T:691 INFO <general>: m_deviceName : Default
2022-01-02 15:42:11.157 T:691 INFO <general>: m_displayName : Default
2022-01-02 15:42:11.157 T:691 INFO <general>: m_displayNameExtra: Bluetooth Audio (PULSEAUDIO)
2022-01-02 15:42:11.157 T:691 INFO <general>: m_deviceType : AE_DEVTYPE_PCM
2022-01-02 15:42:11.157 T:691 INFO <general>: m_channels : FL, FR
2022-01-02 15:42:11.157 T:691 INFO <general>: m_sampleRates : 5512,8000,11025,16000,22050,32000,44100,48000,64000,88200,96000,176400,192000,384000
2022-01-02 15:42:11.157 T:691 INFO <general>: m_dataFormats : AE_FMT_U8,AE_FMT_S16NE,AE_FMT_S24NE3,AE_FMT_S24NE4,AE_FMT_S32NE,AE_FMT_FLOAT
2022-01-02 15:42:11.157 T:691 INFO <general>: m_streamTypes : No passthrough capabilities
2022-01-02 15:42:11.157 T:692 INFO <general>: CActiveAESink::OpenSink - initialize sink
2022-01-02 15:42:11.157 T:692 INFO <general>: CAESinkALSA::Initialize - Attempting to open device "hdmi:CARD=allwinnerhdmi,DEV=0"
2022-01-02 15:42:11.162 T:692 INFO <general>: CAESinkALSA::Initialize - Opened device "hdmi:CARD=allwinnerhdmi,DEV=0,AES0=0x04,AES1=0x82,AES2=0x00,AES3=0x00"
2022-01-02 15:42:11.163 T:692 INFO <general>: CAESinkALSA::InitializeHW - Your hardware does not support AE_FMT_FLOAT, trying other formats
2022-01-02 15:42:11.163 T:692 INFO <general>: CAESinkALSA::InitializeHW - Using data format AE_FMT_S24NE4
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I use the VP9 test image and playing movies, music and Youtube all works well. But I remember that I once had problems with Onkyo and HDMI and resolved it with a new HDMI cable.