Is it possible to use the Dell AC511 volume knob under Slackware?

My Dell AC511 speaker has a volume knob. I have been looking in to
whether it can be made usable under Slackware. With pulseausio running,
the output from
pacmd list-sources >t1
includes the following.
* index: 1
name: <alsa_input.usb-Dell_Dell_AC511_USB_SoundBar-00.analog-stereo>
driver: <module-alsa-card.c>
flags: HARDWARE HW_MUTE_CTRL HW_VOLUME_CTRL DECIBEL_VOLUME LATENCY DYNAM
IC_LATENCY
state: SUSPENDED
suspend cause: IDLE
and later
alsa.driver_name = "snd_usb_audio"

I issued
parecord\
--device="alsa_input.usb-Dell_Dell_AC511_USB_SoundBar-00.analog-stereo"\
--raw parecord.dat
twice, and let it run for ~5 seconds, the first time without turning the
knob, and the second with turning it. Both time the result was ~1M of 0's.

Question 1: Is this the knob device?
Question 2: Is there a driver for this device?
Question 3: Why isn't there any data?
Question 4: What is the format of a volume knob data stream?

Some further information.
lsmod lists snd_usb_audio.
PA_SOURCE_HW_VOLUME_CTRL is defined in /usr/include/pulse/def.h