I had some time today to disconnect my 990 and hook it up to my PC to install the 3.24 firmware.
I listened to one CD for an hour (before update) and then again (after update).
I always use Upsample mode, and re-entered my info back into the 990 after it reset.
I could tell a definite difference right away.
The bass through the main speakers and sub was more pronounced. Fronts were set to Large, 40Hz, and the Sub was set to L/R+Sub, as I have used these setting for 2 years.
I changed the fronts to Small, crossover 40Hz, and Sub to Yes and -10dB.
This now sounded right. There was still noticeable bass, but not nearly as overpowering as when set to L/R+Sub.
Sound quality was still good, and there seemed to be a little more detail in the instruments.
One thing I imminently noticed was that instruments now sound like they are 'in front' of the speakers, instead of at the speakers or behind them.
But instrument also seem to be 'pushed' slightly to the sides and not 'filling' the center as much.
I tried a few other CDs and after a 2 hours I got use to the 'new' sound.
In the end, I would say the upgrade is worth it, as bass management works better and there is more resolution using Upsample mode.
I'm just not sure why instruments that use to be heard in the dead center are now closer to the left or right side of the soundstage.
Not all CDs are like this, which is confusing. If its a small group (quartet/quintet) it is more noticeable than a larger group (orchestra + chorus).

I haven't tried any DVDs yet, so can't comment on how the new firmware will effect it.