Upgraded to 7.0.2.009.Lost my audio on my MXQ Pro(not 4K).
I'm using HDMI for Audio.
When I upgraded the audio device became "Default, Bluetooth Audio Device(PULSE AUDIO)".
But on 008, the Audio device was ALSA based - which worked great.Downgraded back to 008 - everything works OK again.
Sounds like you used the wrong dtb.img file.
I had the exact same thing ( PEBKAC ) - swapping out to the right dtb.img fixed it.