VIBE Powerbox65.4 Car Audio 520W Amp Plug & Play Amplifier for BMW 5 Series E60. VIBE have produced a market leading Plug and Play Amplifier to suit your BMW. A - A channel of an amplifier is for one output, for example a 4 channel amplifier will allows 4 separate products (or more if linked together) so a 4x65 watt amp gives 4 outputs of 65 watts.
eBay