EDIT:
10.6 not work in 3x2 mode , immiadately BSOD
10.4 cant oprate even 3x2 mode
10.5 works GOOD (but need to instal completny new OS or make super clean of old drivers if 10.6 was instaled before)
technically I got 8400x2100 res in 2D
but after when I want run dirt2 and grid, I saw only when dirt2 logo flicker @ main screen and softh @ side screen. After few hours of modify softTH cfg file, I got still the same situation, so I decided to make little experiment and I change resolution to lowest - 800x600 /per screen - stupid I know, but I cant any other option to do so:
1680x2100 + 5040x2100 + 1680x2100
@ 800x1200 + 2400x1200 + 800x1200
so instead 8400x2100 I got 4000x1200
dirt2 run without problem @ first try on the same settings as before I cant run game on 8400x2100
so for now I am totally screwed and dunno wtf, I will try next week in other games
also this is a pic of 4000x1200 (stretched and not look good, but point was - run 10 monitors @ softTH 2+6+2
I used hd5870 2gb e6 + hd5450 + hd5770