Grazie per la ricerca, io quel post non l'avevo visto, ma non sembra risolvere (ho inserito le differenze tipo NoDDC e ignoreEDID).
Ho comunque fatto un passo avanti, impostando nella sezione monitor
codice:
    Option "Enable" "true"
che forza l'attivazione dell'output VGA.
L'errore che ricevo ora e' leggermente ma significativamente diverso:
codice:
(**) intel(0): Depth 24, (--) framebuffer bpp 32
(==) intel(0): RGB weight 888
(==) intel(0): Default visual is TrueColor
(**) intel(0): Option "AccelMethod" "exa"
(II) intel(0): Integrated Graphics Chipset: Intel(R) 945G
(--) intel(0): Chipset: "945G"
(--) intel(0): Linear framebuffer at 0x80000000
(--) intel(0): IO registers at addr 0x90200000
(WW) intel(0): libpciaccess reported 0 rom size, guessing 64kB
(**) intel(0): Using EXA for acceleration
(II) intel(0): 2 display pipes available.
(II) Loading sub module "ddc"
(II) LoadModule: "ddc"
(II) Module "ddc" already built-in
(II) Loading sub module "i2c"
(II) LoadModule: "i2c"
(II) Module "i2c" already built-in
(II) intel(0): Output VGA using monitor section Monitor0
(**) intel(0): Option "Enable" "true"
(II) intel(0): I2C bus "SDVOCTRL_E for SDVOB" initialized.
(II) intel(0): I2C device "SDVOCTRL_E for SDVOB:SDVO Controller B" registered at address 0x70.
(II) intel(0): I2C bus "SDVOB DDC Bus" initialized.
(II) intel(0): Output TV-1 has no monitor section
(II) intel(0): SDVOB: device VID/DID: 02:C2.02, clock range 25.0MHz - 160.0MHz
(II) intel(0): SDVOB: 1 input channel
(II) intel(0): SDVOB: RGB0 output reported
(II) intel(0): SDVOB: CVBS0 output reported
(II) intel(0): SDVOB: SVID0 output reported
(II) intel(0): SDVOB: YPRPB0 output reported
(II) intel(0): SDVOB: SCART0 output reported
(II) intel(0): I2C bus "SDVOCTRL_E for SDVOC" initialized.
(II) intel(0): I2C device "SDVOCTRL_E for SDVOC:SDVO Controller C" registered at address 0x72.
(II) intel(0): No SDVO device found on SDVOC
(II) intel(0): I2C device "SDVOCTRL_E for SDVOC:SDVO Controller C" removed.
(II) intel(0): I2C bus "SDVOCTRL_E for SDVOC" removed.
(II) intel(0): Current clock rate multiplier: 1
(II) intel(0): Resizable framebuffer: not available (1 3)
(II) intel(0): Output VGA enabled by config file
(II) intel(0): Output TV-1 disconnected
(WW) intel(0): Unable to find initial modes
(EE) intel(0): Output VGA enabled but has no modes
(EE) intel(0): No valid modes.
(II) UnloadModule: "intel"
(II) UnloadModule: "vgahw"
(II) Unloading /usr/lib/xorg/modules//libvgahw.so
(EE) Screen(s) found, but none have a usable configuration.