There is a distinct lack of bass on a surround system. I would usually use -36dB on my Yamaha amp but with this game it's up to -30dB. PC1 however was very loud but the mix was better at -40dB.
They've put rear engined cars to the rear surround speakers which is fine in theory but when you look at most 5.1 setups the rear speakers are satellites which don't have the same bass response as front speakers so the mix is very flat. My setup is 2 large Monitor Audio floor standers left and right with smaller speakers for the centre and rear speakers.
If you're in a rear engined car you don't just hear engine noise from the rear as the sound travels around the cabin. The sound design and mix needs to reflect that.
The update has been a lot better for me bar sounds. Being able to actually choose setups now is great. Not sure why the cars aren't set to stable by default. The ginetta is actually very predictable now. I feel like the FFB has been tweaked also as I'm getting a lot of information about what's happening. This may be because I've come from the GT Sport demo which is a little numb in comparison. I still personally wish it had a little more strength to it.
Bingo... there is nothing in the mix below 120Hz regardless of where the mix is coming from spatially. For example if the sound is coming from satellite rears that are unable to extend below 120hz then the crossover set at 120hz or 80hz or whatever you set your specific crossover at should route that frequency to the sub.
The issue is there is nothing to route below 120hz or there abouts... so there are simply no bass frequencies to amplify for a tactile transducer or subwoofer. This is my experience on PS4. I wonder if PC users have the same issue or completely different mix altogether.
For example if you watch 650s GT3 videos on youtube on PC, the cockpit sound is very different. The 650s gt3 on PS4 cockpit sound is like a lawnmower, there is very strange garden mower sound that isn't present at all in the PC videos.