First, your two links are DEAD.
Second, yes it can be done quite easily... but you need to use the same audio device for all the speakers.
Assuming you have a built in sound on motherboard (or soundcard)... I'm going to guess you have your Logitech speakers plugged into the Front Audio ports, right? You need another cable to plug your monitor's audio IN with the REAR AUDIO OUT from the same soundcard port... so in other words, both cables from the Logitech speakers and monitors are right next to each other.
If you do it like that, your Logitech speakers would be your main/front speakers and the built in speakers from your monitor would be your rear speakers (or vice versa).. and you would end up with a 4.0 Speaker System... (four channels)