I did a trip return trip from Brisbane to Toowoomba yesterday. I loaded a 32Gb USB stick into the usb A port in the cubby. After a 45 second fiddle with the "settings" and a re-balance of the speakers to take account of the load of stuff in the cargo area I found the stereo to be more than adequate. I was listening to the Caxton St Jazz Band, Kiri Te Kanawa singing jazz, Al Bowley, some works by Chopin, Tchaikovsky's 1812 . The base was adequate, the mid range surprisingly clear and the treble ranges more than adequate. I did wind the window down at one stage to listen to the diesel "purring" as it propelled the vehicle up the 10% grade on the Toowoomba range
...that was music of a different kind! What with the noise of the engine and tyres on some surfaces competing with the music system, I'd say that the standard offering is quite satisfactory. A small subwoofer might give little more depth but it's neither urgent nor important in the scheme of things. I have a sensitive ear for "matters musical" and I doubt I'll be spending additional funds on the stereo .