My way of getting Trus Mico to work reasonably on FreeBSD was using pulseaudio, and remapping the pulseaudio input source to mono.
First look in the dmesg to identify where the device ends up:
Trust Mico is the C-Media device on uaudio1 in this case
As you can see, uadio1 ends up on pcm4
Now we know that the Trus Mico is the C-Media device on uaudio1, and that uaudio1 is connected to pcm4
In case you have pulseaudio installed, you can try this in a terminal:
pactl list sources
Somewhere in the output I found:
/dev/dsp4 is the dsp corresponding to the pcm4 device
The pulseaudio source name for this device is listed as:
Now one can try:
pactl load-module module-remap-source source_name=mono master=oss_input.dsp4
In case everything works, now a new input source should be available after starting pavucontrol.
Now I can set the volume on the new input source (I have it around 125%)
I really hope this works for you too