also, keep in mind of the harness adaptor needed, it is listed as VW and porsche but fits rover. you must use the RCA conversion plugs in the kit if you use the factory amp, this allows for subwoofer function. also you must connect the power antenna wire (normally blue or blue with stripe) as it turns on the amp and antenna reception amplifier as well (otherwise no radio reception).
when using this harness, keep and eye on the yellow and the red wires as on german cars they are reverse operation, that is on many vehicles the yellow wire is constant power for memory functions, on german the yellow wire is key power.
if you're bypassing the plug at the dash, you need to run speaker wires straight from the head unit to each speaker. and you loose the sub woofer function. personally I use the adapter plug harness, solder and heat shrink connections, that way there is no wire splicing into the vehicle thus less chance of mishaps.
there is always a bit of buzzing when using aftermarket head units, partial solution (you will never fully get rid of it) is to clean your grounds, some radio installers advise to run a new ground from radio to body. this did not work on mine.