aplay --list-devices
**** List of PLAYBACK Hardware Devices ****
card 0: PCH [HDA Intel PCH], device 0: CX20590 Analog [CX20590 Analog]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 1: HUDmx2 [Audinst HUD-mx2], device 0: USB Audio [USB Audio]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 1: HUDmx2 [Audinst HUD-mx2], device 1: USB Audio [USB Audio #1]
Subdevices: 1/1
Subdevice #0: subdevice #0
We want whatever is [Audinst HUD-mx2], device 1: USB Audio [USB Audio #1]. We can see it belongs to card 1, device 1, which translates to: hw:1,1.
pacmd load-module module-alsa-sink device=hw:1,1