Audio output from HDMI can not be forced with hdmi_drive=2

I am new to this forum and to the Raspberry.
I have a Raspberry 4 and just installed Volumio. I try to hook it up to my MiniDSP‘s Hdmi Input. The MiniDSP has a somehow undefined EDID signal. I tried to override the HDMI sensing with hdmi_drive=2 and hdmi_force_hotplug=1 but I get no sound out of the Raspberry. I then attached the Raspberry to my Oppo 103 with a tvscreen hooked up. When I started the Rhaspberry it did enable audio over Hdmi and all is fine (as the EDID is good now)
So it seems that the line hdmi_drive=2 does not help, neither does hdmi_force_hotplug=1.
The Raspberry 4 has two Hdmi outputs and I am thinking, that the HDMI commands are probably wrong and need a 0 or 1 to adress the specific ports. Any ideas?

So the problem is the strange EDID response from my NanoAVR. Hdmi workS when booted into an Oppo 103. I can swap the HDMI cable into the NanoAvr after the boot and it works. There is still something strange with the configuration setting, nothing made the R4-HDMI to boot into my NanoAvr correctly.
But - the Hdmi output sounds not good. There are posts explaining that certain video modes are better for Audio than others, as the frequency multiplier employed for embedding Audio into the Videostreaming works sometime better for audio. Would anybody have a suggestion for a good video mode giving good audio?