This is an odd one for me, as it comes across as less broken and more an issue with the dynamic range.
I run a circa 2k AV system and have gotten quite used to having to adjust volume levels depending on the source and how it's been recorded, mixed and compressed (if it's been compressed).
Now a couple of background bits, heavily compressed audio has a low dynamic range, which means that the volume difference between the quiet and loud bits are smaller. The less compression, the higher the dynamic range and the greater the volume difference between the quiet and loud bit. This is a massive simplification, but it's good enough for what I'm talking about.
So if I play a film on Blu-ray with uncompressed audio I would have to set the AV reciever to around -10 dB (on a zero dB scale) to hear the soft speech, but any explosions, gunfire etc would be amazingly loud. However if I put on a DVD with an old Dolby Digital mix (which is heavily compressed) then the volume would be closer to -25 dB and the difference between quiet and loud much less noticeable.
Many people have come across this with night modes, which compress the audio, allowing you to hear a range of volumes at a lower overall volume.
Many game titles give audio output options allowing you to vary the degree of compression. With TV, headphone and night modes having the greatest level of compression, and 7.1, 5.1, large speaker and AV modes having the lowest level of (or no) compression.
Interestingly one of the first titles I can recall offering this was GT 5 prologue.
However the issue with PC2 seems to be that it's locked to a high dynamic range, which is fine if you have an AV system that can deal with it and don't mind pissing off the neighbors. However it's a big issue if you don't, as it means that it's both too quiet overall and detail also gets lost.
For reference I run roughly the following volumes across a range of titles.
Project Cars -38 dB
Project Cars 2 -27 dB
AC -32 dB
Dirt -32 dB
GTS -35 dB