I’ve got a 5000C. The volume goes up and down on that in unison with the front analogs no probs when I’m watching movies or listening to Trifield using any of the volume control devices.
Sounds fine to me but expect there are settings in the 218 config that can be used to fine tune things.

HT: 861v8 - ID41, HD621, DSP5500hc, DSP5000 front, DSP3100 S&R, REL t9 SW.
Office: Fanless 7i5 w/ ROCK, 218, Woo Audio WA2, Focal Utopia HP’s
Family Room. Grandinote Volta, Grandinote Shinai
Bedrooms: Allo digi, 3100C, Prime HP amp & PS
BBQ/Party: Raspberry Pi, Explorer 2