Sound Check in iTunes 10.6 is different versus Sound Check in iTunes 8.2

Hi. My OS is Windows 7 Pro-64.

I have lots of CD and I decided to convert them in an mp3 library imported in iTunes (and “manually” in an iPod Classic) with Sound Check on (either in iTunes, or in iPod). I managed it with Windows XP and iTunes 8.2 till last year. I always verified the Volume adjustment of each mp3 and the correlated hex values written in the field iTunNorm (using mp3Tag). So far I was quite satisfied of Sound Check because I use iPod like a “juke-box” (I don’t need a per album normalization).

Last year I updated to Windows 7_64 and to iTunes 10.6 and I went on importing other mp3 files (from my CDs). But, with some test, (I imported the same file using iTunes 8 on a PC and using iTunes 10 on a different PC) I realized (with a very high probability) that:

1. iTunes 10 apparently don't write iTunNorm tag anymore in the file mp3. I have a Volume adjustment, but with mp3Tag I can’t read any iTunNorm field with the famous ten hex values.
2. iTunes 10 and iTunes 8 use a different way to calculate Sound Check; Volume adjustments calculated with iTunes 10 are lower of about 0,75-1,25 dB in average against iTunes 8. But sometimes the difference may be very high (-3,5 dB or -5dB for example in iTunes 10 versus iTunes 8).
3. When I updated to iTunes 10, my old library has been converted into the new format iTunes 10, but the old Sound Check (calculated with iTunes 8) did not change (no new calculation). So when I add new files to the library with iTunes 10, I have a discontinuity with the old files imported from iTunes 8 as far as Sound Check is concerned: the new files sound lower in average than the old ones.
   
   I don’t want to delete and re-import all my files in order to reset and homogenize the whole library (I’d lose all statistics and I’d waste lot of time to pass the file in iPod). And I don’t want using third part software like iVolume.

My questions:

1. Is it correct what I wrote at the point 1, 2, 3 stated over here and mainly at the point 2 (Different way to calculate Volume adjustments of iTunes 10 versus iTune 8)?
2. Did iTunes 10 stop to use iTunNorm field to write Check Sound info in mp3 files?
3. If not, where iTunes 10 write Sound Check info to the mp3 file and how can I read it?
4. What can I do to avoid the discontinuity in Sound Check values due to the use of iTunes 8 and iTunes 10?

Thanks in advance for your answers.