There is always the option of adding any aftermarket amplifier and speakers you want. General principles of installation will apply:
*powerwire for amp from battery, fused
*groundwire to chassis
*remote trigger (ignition) wire to amp
*audio signal connection to amp: can tap into speakerwires and use a line output converter
*new speakerwire from amp to speakers: can run wires to existing Alfa speakerwire ISO plug
*speakers mounted on mdf wood spacer rings
Plug-and-play can offer a minor improvement. Much like Bose is better than the standard system. But aftermarket gear has much great potential. It just requires a bit more technical installation and tunings.