I've recently spent about £400 on upgrades to my in car sound (Toyota Camry).The items I have added have all improved the sound but the degree of improvement each brings is varied. This is just what I thought of my new toys. I have a good head unit already. A Kenwood Z838W which does very good mp3 and is rated at 50W x 4. In reality that means 25W+ rms per channel. I asked the question here as to wether the head unit could drive component speakers and was told yes but they would sound poor compared to driving them with an amp. The car stereo dealer told me something very similar. I bought a Kenwood amp (£200) and some infinity 6 1/2 component speakers (£100) for the front, along with a cable kit. The amp I chose was 5 channel so that I could add a sub if I felt I needed one.I have an electrical background so installing it all did not worry me. The weather turned bitterly cold around the time I bought the stuff so I did not rush to get it all installed. First thing i did was pull the doors apart and fit the speakers.This turned out to be quite easy as the existing speakers were components (although I've never heard the tweeter) and all the mountings were in place. I ran the Infinitys off the head unit as i had no time (or heat!) to do more of the install. What a difference! The infinitys transformed the sound...really clear and detailed by comparison. I had to turn down the 6x9's at the back so they did not spoil the sound. The infinitys are far less sensitive than the OE speakers so the head unit volume setting was higher but the sound was fine. I can say that the advice I had was wrong. 25W rms is enough for a good sound from components.It would go as loud as I could ever want without hitting distortion.Bear in mind I was after improvement at 'normal' listening levels. As I already had the amp i carried on at leisure and finished the install. 40W rms made no noticable difference at 'normal' levels but it did extend the distortion free sound to uncomfortable levels.The 6x9's still sounded poor. The amp looks like one giant heat sink so i was concerned it might get hot. After a normal journey (40 mins) it is pretty near stone cold! Having gone that far I thought I might as well finish the job and get a sub. There was a 'anyone know this sub' thread here which was a good price on an infinity sub. having been so pleased with the infinity components it seemed as good a bet as any.I didn't quite reasilse from the picture what a big bugger it is! Fortunately the boot on the camry is pretty big so it swallows it OK. The amp has 120W rms on its sub output which may be considered lightweight for the size of the sub... but it drives it fine as far as I'm concerned. I want it to add the bottom end bass not impress the street when I drive past. Listening to the sub direct whilst tweaking the levels on the amp.. it sounds more Kef PSW2000 than Velodyne CHT-10. At home the Kef had to go... in the car I can live with bass with a rumble to it. I've never had an amp or sub in a car before. If I was starting again I think I would go straight for the component speakers and an active sub or amp+sub.I think the need for an amp depends on how loud you normally listen and the quality of the head unit. I may have spent a bit more than I needed to but overall I'm pleased with the result. If the urge kicks in again i may change the 6x9's but for now I'll leave them turned down.