Allows direct interface of any pre-amp level audio source to a factory radio with a slave unit, eliminating the need for sound-degrading solutions like an FM modulator Interfaces input sources from DVD, VCP, MP3, satellite radio or PlayStation Lower cost & higher quality sound than an FM modulator Comes with a 3-position switch between 2 aux inputs & the factory slave unit High-quality audio isolation IC eliminates engine noise Internal CMOS electronic switching for long-term reliability Requires factory XM Satellite Radio receiver, factory DVD rear seat entertainment or factory/aftermarket CD changer In order to work, slave unit must continuously be playing or XM Satellite Radio or DVD, must be on For 2003 GM Class II