LCD Heads Up & Amps / Speakers in M5

[beldecca]

OK, I know that the HU is not the best in our 5's.
Certainly Mazda does a nice jobs of making it seamless with the dash which also makes it a pain to replace.

So here are some questions (some of which might have been asked before but not wrestled enough). I appreciate any ideas people might have. Crutchfield is annoying me and I'd like some input from someone who isn't trying to sell me something.

I really like the little LCD panel (thingy that says "hello") and find it a great location for caller ID. Is there anything out there that has better sound that the stock radio that will talk to the LCD?
Could the LCD be connected to a carPC?
(I'm going to assume "no").

I'm new to car audio.
(a link to what I tend to listen to: http://www.youtube.com/watch?v=G1s1BkjLj84 Thievery Corp - The Numbers Game)
With that, which is the best way to go with upgrading the M5's sound staging?

1. Speaker upgrade?
(adapting to a 6.5" round - better for speakers?)
2. Speakers + amp?
3. Sub only
4. Speakers + sub + 5 channel (or 4 channel and a mono amp)

Also, does brand matter that much? Certainly don't want anything too cheap. But is Kenwood / Pioneer going to be ok. Or do I need JL / etc.

If I'm looking at sound proofing (Dynamat vs something else?)
- is it ok to do it piece by piece - or -
- is it best to rip everything out once and do it then (is the carpet glued?)
(any idea how much I will need)

Ok, I know that was alot. Tackle what ever part you want. Thanks for your time.

 

[bootman]

You will lose the LCD interface when you replace the HU. (A/C info will be there along with the clock.)
There is nothing available that will let you hook up to it.

The stock speaker size is 6x8 so most beefy 6-1/2 will be a tight fit.
A 5-1/4 will always fit or get a good component set that has a 6x8 woofer.
One of the best online resource on what will fit exactly is crutchfield.
Not always the best price, but they have outstanding support.
Almost a no brainer when something is on sale.