Drivers are software. The BIOS is firmware. For the Pegatron B85-M2, updating BIOS is unless you have boot failures or unsupported CPUs (e.g., Xeon E3-1285 v3).
If the audio driver installs but there is no sound, check the BIOS to ensure the "Onboard Audio" is set to "Enabled." pegatron b85-m2 drivers