Retropie 4.3 with Gert VGA 666 blank screen in emulators

[Bublina]

Hello, I'm trying to get working latest Retropie 4.3 on Raspberry Pi 3 with Gert VGA 666 adapter.
I downloaded image from official Retropie site. I'm using 5V/2.5A PSU, USB gamepad and VGA LCD monitor 1024x768.
I followed guide on raspberry pi forums: https://www.raspberrypi.org/forums/viewtopic.php?t=94424
I added following lines into my config.txt

dtoverlay=vga666
enable_dpi_lcd=1
display_default_lcd=1
dpi_group=2
dpi_mode=16

When Retropie boots up, I can see boot messages on the VGA screen and then Emulationstation starts up.
After the first boot, I successfully configured my controller. I uploaded some ROMs over WiFi, but when I start any of the emulators (I tried MegaDrive, NeoGeo and MAME and KODI so far) the monitor connected over Gert VGA 666 goes blank. If I press Start + Select, the screen returns to the Emulationstation. It seems, that the emulators and KODI are running on some other screen. If I connect HDMI screen to the Pi and remove the code above from my config.txt, everything works correctly.

One more thing I noticed - If I have connected the screen via Gert VGA 666, video previews in the emulator menus are not working, only black rectangle is shown. Video previews works OK over HDMI.

I'd like to ask, how I can get emulators working over Gert VGA 666? Thanks in advance :)

[EMaDeLoC]

I have very little experience with VGA 666 (in fact, I tried for first time today... ^_^U) but I have no problems with any emulator. I can give you some advices, maybe it works with you, if you still have problems.

Set dpi_mode in hexadecimal format, in your case 0x10 as it's listed in this table, just in case:
dpi_mode=0x10

Set framebuffer to your desiere resolution:
framebuffer_width=1024
framebuffer_height=768
Comment any HDMI config line:
#hdmi_force_hotplug=1
#hdmi_group=1
#hdmi_mode=1
#hdmi_drive=2

Kept this lines commented:
#dtparam=i2c_arm=on
#dtparam=i2s=on
#dtparam=spi=on
Or if you want, uncomment turning off everything:
dtparam=i2c_arm=off
dtparam=i2s=off
dtparam=spi=off

Try some other VGA modes, like 75hz (0x12) or 800x600 (0x09, 0x0B).
Be sure emulators are not using special scaling resolutions than may be incompatible.

Last one, universal solution to any computer problems: install retropié again and try with default retropié configuration.