ok, I'm running my epia direct to a amp, then to upgraded speakers.. I dont know what the original speakers sounded like.. so cant comment on that.. All I know is that its sounds awesome. If you fancy keeping your original sony unit and speakers,I would prob relocate you headunit into your glovebox, and use the AUX input on it to stick your carputer into it. You can also get a magicbox that will allow you to link your steering wheel controls to your sony unit. If your sony unit doesnt have a aux in, you can buy I little sony box that will allow you to do this and also can be linked via USB direct to your PC.. (I did this in my last install). As for how long does it take.. well how long is a piece of string.. lol It took me a couple of weeks of messing about but I had done one before so had some idea where I was going. As for boot up time.. my system wont hibernate because of the dlink radio, so it takes about 30sec's to boot, which isnt to bad.. I get to the end of our road and its normal up and running by then. As for making the dash trim.. it wasnt to hard at all, more time consuming really. As for the cost.. its hard to tell but about £700 something like that.. thats including everyting (except the amp and speakers.. thats another £1000 on top). Compare this to the price of a kenwood or alpin gps system that still wont do everything mine can do its not bad at all .
Hope this helps you