I'm looking for 2.1 computer speakers but none of them appeal to me in their asthetics and lack of optical input. I was thinking about the Logitech Z906 but it's a 5.1 sound system because it has optical inputs and it comes with a more powerful subwoofer and speakers than the Z623. I only have space for 2 small speakers and a subwoofer. Can the Z906 be configured for only 2 speakers and a subwoofer? If I only use 2 speakers from the Z906 would I still be able to get Dolby Digital decoding without missing sounds if I use the optical input?