(I know subwoofer issues have been discussed earlier but I couldn't find one to answer my problem).

I am working as an IT- and AV-support in a school. That way I have some nice gadgets lying around and I try to make use of them. In my office I have a Beomaster 4500 + Beogram CD4500 with Beovox 3000 flat-panel speakers The speakers are fine but they lack in bass as of their size and type.

I have an excellent Genelec active subfoower available so I'd like to connect it to the system. I have done it by taking the signal from the powerlink socket (combining L and R-channels) but this causes the main speakers to work in mono, too! I can run the system fine if I only take one channel to the sub (listening to it right now, sounds absolutely fantastic!) but I guess it's should have both channels there. Any ideas?

Yes, it will play in mono as you are essentially shorting the channels together after the preamp... try something like this (I use the same CAD program as Jaff).