V90/XC90/S90 HK AUD .VBF Files

[IMAY2023]

Which MIDs and Highs are louder? Front door or rear door? 
On front doors, gen2 has MIDs and High separated.  This means the minimum output impedance of the AUD for each channel might be lower than gen1. 

MIDs and Highs are in parallel on Gen1, the total resistance of the (MID +HIGH) speakers are little bit more than 6 ohms.  If I remember correctly.  
You need to know what is the resistance of the new gen2  MIDs and tweeters then you need to match them with your current speakers. But still, you will need to rewire the fronts.  For the rear ones, you need to measure the combine resistance of the gen2 and then match yours if there is a difference. 

As I said in the beginning, unless you got the gen2 AUD for free, it does not worth it if you already have gen1 B&W.

IMAY2023, thank you. You are absolutely right.
They are all louder (center and front - much, rear and celling - less) with the Gen2 amp. I see that the speakers in the front doors and the center speaker don't have capacitors in Gen 2. That's ok, I can replace them on occasion. I have several speakers with silver cone, but not a full set
But what about the amp's software?

Your AUD already has the software inside it. You don't need to change it. As far as I know, the software inside the gen2 B&W is same for both 60 and 90 series. The wiring and the channel outputs of the gen2 B&W AUD are same for both 60 and 90.  The only difference is the MID range on the rear doors which are parallel to tweeter. Now, there might be some configuration changes where MID frequency is moved from low (woofer) to High (tweeter) and the rear door woofer on 60 series are different than 90 series since on 60 series it responds to wider frequency range than the woofer on 90 series. 

Having said all this. 
There might be some differences in the IHU's software "Sound Experience" application. 
The IHU is connected to AUD via MOSTs the commands are sent to AUD from the IHU. Now, your current IHU might send commands to AUD that are not recognized by the gen2 B&W.  For example: My IHU does not have the Juzz club. It has the concert hall. If I connect gen2 B&W, it might not work.  Or the Equalizer frequencies might be different on your IHU but gen2 IHUs are different.  For example, when I changed the setting to premium audio, without replacing the HK AUD with B&W one, the basic audio settings worked perfectly. The sound was pre-amped much better, However, the sound experience app was acting weird. The AUD was not always reacting to changes between studio or surround.   
Of course that is just a possibility,