ASUS A8N-E Realtek S/PDIF

Yo everybody. Im hoping someone will have a fix for a sound problem im having with audio drivers for my Mobo ASUS A8N-E. Im using the most recent Realtek drivers (A4.00) but everytime i go into the speaker config and select 6 channel ouput i dont receive true 5.1 surround sound. In fact if i watch a film with this setting turned on then i begin to lose some audio. Im using an optical out cable to my Logitech Z-5400 speakers. Even if i run a test for the 6 channel it only every picks up the front right and left speakers. It wont even pick up the center never mind the rear two. If i leave the channel setup to 2 then i will recieve audio to all speakers but it isnt true 5.1. :confused: Heres another point, if i use the analogue connectors to the Logitech from my PC it does pick up all the speakers albeit not in the right order. I would hate to have to change over to the analogue as music and film audio quality is much improved using the digital optical cable (much louder and crisper). Any ideas?

Thanks in advance.