sub is and isn't working

[QuAtT]

I've got 5.1 sound system (genius, I know it's shit beyond believe) plugged into a genius 5.1 sound card(shit again, but it does the job) and the sub isn't working as it should
the sub is working when I set the system input on 6CH ang than I watch mvies with 5.1 surround sounsd (It also works if I set the system input on 2CH)
but when I watch youtube videos (2 channel sound) the sub isn't working (even if I set system input on 2CH, which expands sound on all speakers)

so what do you guys think?

[Tu154M]

Did you set the output to 6 channels?

[QuAtT]

[QUOTE=Tu154M;28187789]Did you set the output to 6 channels?[/QUOTE]

yes I did

[Fatal-Error]

my bass is just plugged into my center channel.
Works all the time regardless of mode.