Install the alsa-utils package make sure your user is part of the audio group to access audio devices.

# xbps-install -S alsa-utils
# usermod -a -G audio <username>

The alsa-utils package comes with the system service /etc/sv/alsa which can be activated to save and restore the state of alsa controls like the volume at shutdown and boot respectively.

If the soundcard you want to use is not the default you can either use kernel module options or the alsa config to change the default card.

The current module order can be retrieved from the procfs filesystem.

$ cat /proc/asound/modules
 0 snd_hda_intel
 1 snd_hda_intel
 2 snd_usb_audio

To use the kernel module options you can create a file like /etc/modprobe.d/alsa.conf with following content.

options snd_usb_audio index=0

Alternatively using the alsa configuration file /etc/asound.conf or the per-user configuration file ~/.asoundrc to set a different card as the default.

defaults.ctl.card 2;
defaults.pcm.card 2;