I think I have the Midline sound system but could you confirm

Its got bass units and tweeters in the front doors, speakers in rear door (Not looked to see what they are) and a sub in the boot. On the door speaker grill is Alpine.

Will there be a separate amp or is it just the head unit that feeds the speakers?

The problem, for me, is the soundsatge is crap plus I have had to turn the trebble up to max and it still sounns not very clear. I have head others say the system sounds dead, I would agree.

I was going to buy some better quality speakers but have discovered the bass drivers in the doors are 2 ohm and the tweeters are about 3.5 ohm so unsure what to do

Not sure if I am going to answer your question but would like you to confirm what source you are using? I have found that the cd is far superior to aux socket MP3s, but you may know that already if you are talking about sound stage. I have MY07 with Dolby surround 6 disc, not sure I have found all the speakers but there are at least 11 and they have Alpine on them too. It has a good sound, not particularly hifi, but good enough for the car.

I have discovered that the sub-bass is much tighter with a proper spare wheel in the boot

Thats probably how it was designed and taking the spear wheel out spoils the sound

Also, as said, it depends on the source quality. Different Mp3 bitrates will sound differently, try a proper cd.
On analogue Radio, the sound is very thin, i have heard the difference to DAB, its way above, so the mid line systems sound depends definatly on the audio source.

I am fine with the system, hearing rock and metal \m/

However this has not answered my question. Is there a separate amp?

Isn't there an amp in the boot behind the o/s panel .

Yes, found it thanks

I have started a new upgrade thread http://www.freel2.com/forum/topic22368.html

Bit off topic but evidently top end Porsche turbos and Ferraris don't come with a decent (or any) radio as you are supposed to listen to the sound of the engine.

Had my first proper drive and tried a CD, much better. Why is the radio so bad?