Find great deals on eBay for onkyo powered subwoofer. Shop with confidence. Skip to main content. New Listing ONKYO SKW-204 10' Bass Reflex Powered Subwoofer, 230W Black- Pre-Owned. 1 product rating - Onkyo SKW-770 Single Powered Black Subwoofer 163 Watts VG Condition! Powered Subwoofer SKW-770 Instruction Manual Thank you for purchasing an Onkyo powered subwoofer. Please read this manual thoroughly before using the unit. Ears are less sensitive to very low bass sounds, there’s a temptation to set the level of the subwoofer too high. As a rule of thumb, set the subwoofer.