Onkyo HTS3500 Speaker-Receiver combo question

Hi guys,

I have bought http://www.amazon.com/Onkyo-HT-S3500-5-1-Channel-Theater-Receiver/dp/B0077V88V8 (not super expensive, but decent-good home theater system).

If I connect my laptop via audio cable (aux connection, Red/White cable), is there a way to force the receiver to play all 5 speakers?
Currently it only plays Front-Left and Front-Right only + Subwoofer. I know it depends on quality of song I am feeding to the receiver, 2.1 encoded or 5.1, but most songs I've found (mp3, Spotify etc) are 2.1 audio channel, so I was wondering if there's a way to get it to play all speakers. My laptop doesn't have a HDMI out.

Thanks,
K3T

I believe it does play 5.1 when fed a hdmi input (say from a cable box or game console), just not sure how to make it happen with laptop (with no hdmi output)

Thanks for the reply tho