Thank you for your quick response.
I have to disagree with your assumptions regarding the use of filters.
Using an NDx2 filter (50% transmission of light), for nearly a year with my 10 HT has done wonders to this projector.
After properly calibrating this projectors using some techniques offered by Mr.Munsil, I menaged to improve the contrast and the white balance of the projector, but the problem of the black level remained.
Reading through a forum dedicated to the wonderful Sony 400q (I miss you, old friend...), I found out that people are using ND filters to improve the black level.
After some experimentation I decided on a filter which allows 50% of light transmission, leaving the projector bright enough, and improving significantly the black level, by turning the Gray "space" into light black. I must say that many people that visited my apartment were very skeptical at first, but once they saw the difference they admitted that this makes a very big improvement. Dark scenes that once were glowing Gray, and could not be watched, are now much improved.
One more point I have to make is that strangely after placing this filter, and re checking my settings using Avia, I found I had to LOWER the contrast by aprox 10%!
After reading through YOUR posts re Gray paint I decided to paint my white wall Gray, which also contributed to the black level, and also helping with ambient light.
But, I still wonder if painting the wall with much darker Gray, would give me a better result then the Filter/paint combination.
I would be glad to read your comment on the above.