How to increase sound volume on eMac P69 running FreeBSD 10.3?

Question

I've got FreeBSD 10.3 (PowerPC) installed on eMac P69.

I'm using MPlayer to test loudness. I already use -af volume=10:1-like options but they tend to distort sound pretty quickly + it is not really a solution.

From what I read online I should be able to change volume using systcl hw.snd.vpc_0db or mixer(8). Unfortunately:

• systcl hw.snd.vpc_0d=45 is too quiet
• systcl hw.snd.vpc_0d=10 is quite ok but still it could/should go louder
• systcl hw.snd.vpc_0d=1 is distorted and really not that louder than 10

• mixer returns:

  mixer: /dev/mixer: No such file or directory

From what I remember when this machine still had Mac OS X its speakers were way louder comparing to what I get on FreeBSD.

Questions

1. Why is /dev/mixer missing?
2. Is there any other way to increase speaker volume?

Other details

They might come in handy:

• /boot/loader.conf

  sound_load="YES"
  snd_driver_load="YES"
  

• I tried kldload snd_hda but it didn't help.

• kldload snd_driver results in

  kldload: can't load snd_driver: No such file or directory

  Also, there are interesting messages in the system message buffer displayed with dmesg:

  link_elf: symbol isa_dma_release undefined
  KLD snd_driver.ko: depends on snd_sb8 - not available or version mismatch