I have 2003 X-Type 2.5L AWD with premium sound but no navigation. I am a bit confused about what is in my car and haven't had time to look either inside the car I mean.

From what I read my car has 9 speaker system. I am guessing 4x tweeters, 4x speakers and subwoofer in rear shelf. I am not sure if my car has an amplifier though. Apparently the entertainment system is hooked up via the D2B network which uses fiberoptic cable.

What I want to know is whether I can upgrade the speakers in my car because the ones currently don't sound that great even on full volume. So I have a few questions I don't know if any of you can answer me.

1. Does my car have amplifier? If so how many watts is it?
2. If I want to add an amplifier to the car or replace old one (if car already has an amplifier), is the wiring already in place or will I have to rewire again because of D2B network fibre optic cable.
3. Can I change my current car speakers to ones with higher watts for better sound quality? If I can replace them, can I use the old grill with them but just change speakers.
4. What size speakers and woofers shall I use, I looked on crutchfield and it
recommends 6.5" with 2.5" depth for front and rear speakers and 10" with 5" depth for woofers?
5. Also I am a bit confused about how tweeters work. If I upgrade my speakers to 3-way ones with tweeter already built in them, Can I use my old tweeters also and connect them to the new speakers, Will I need to?

I am new to car audio upgrades but have done some electrical work before and I am an amateur at this. Would be grateful if someone could clarify it for me. Been reading a lot of guides etc so am keen but please forgive me if i ask basic questions.

Looked at these on eBay they looked good and cheap.
http://www.ebay.ca/itm/350657924828?...84.m1423.l2649
http://www.ebay.ca/itm/130845032434?...84.m1423.l2649
not sure if they'll fit though. according to crutchfield they should.
Also saw this amplifier.
http://www.ebay.ca/itm/370765676042?...84.m1423.l2649