Has anyone installed a amplifier to the factory head unit? I am going to install some better speakers soon and do some major sound deadening in the doors at the time but I have the feeling the Headunit might not have enough grunt. There is a little Alpine amp I have my eye on. Not keen on replacing the head unit for heaps of $ and loosing some of the functions I have now with the existing unit. Just want a bit better sound and a bit louder. Any ideas?.?