A:Answer The ONYX STUDIO 2 should work on aux while plugged in. It seems that your unit is not behaving as it should be, if the unit is within 30 days from purchase, please do contact best buy for a replacement, if it is outside the 30 day warranty of the retailer please do submit an email case to www.harmankardon.com/contactus and our customer support team will assist you on the warranty.