My 2 cents follows :

Spend good money on your amp(s). I would go with Rockford Fosgate, or JL Audio.
the JL amps are VERY clean, the Rockfords really have the Juice.
If you are going to buy Rockfiord Fosgate, make sure you buy the POWER series and
stay clear of the Punch series. BIG difference, you'd be shocked.
I know, I know you're saying "but, dave, I have Punch amps, and they rock"
not always the case...
Rockford makes 2 lines PUNCH and POWER. The POWER series is great.
Then there are 2 batches of PUNCH amps some that go to authorized dealers,
install shops, etc. those PUNCH amps are OK,
but then there's the PUNCH amps you find online for a good price,
or at the department stres, those are no good the only good way to know is to
check the birth certificate that comes with the amp and see that it was tested
at something like 20 percent more than its power rating,
so if you have an 800.4 that amp does 200watts RMS x 4 channels at 2 ohms
for a total of 800watts, a good 800.4 will test at around 1000 watts,
depending on what the voltage was at the time of test.

A nice beefy amp will make all the difference.
I put in that 800.4 in my Accord and it was my plan to
replace all factory speakers,
then I was real impressed at the difference it made,
I still haven't replaced the factory speakers.
Not that I don't recommend it, or that I'm not going to
I mean aftermarket speakers are THE way to go, for sure,
but get a good beefy amp.

If you are going to really want to crank it up,
then I would suggest that you get a separate amp for the subs.
Reasonbieng is that with a 5 chanel amp when you turn up the volume,
the subs really suck power out of the amp,
which can sometimes take away from the power to your other speakers,
thus leaving you speakers underpowered (more about that later)
I would get a 4 channel amp for in the car,
and a 2 channel amp for the subs.
Mono sub amps are good, but later they (might) offer less flexibility.

Pay attention to OHM ratings.
the Rockford amp does 200watts x 4channels at 2 ohms.
Well, chances are you'll only have a 4 ohm load on each chanell,
so that amp is really only gonna give you 100 x 4 at 4 ohms...
see how that works ?

Conversely, JL makes a 300/4 which is 75 watts x 4 channels at 4 ohms,
so you really have to pay attention, you definately want a 4 ohm load.
Since most speakers are rated at 4 ohms.

50 watts per channel at 4 ohms can make you deaf if it were done right,
75 watts is good to have, so you have a little more juice in reserve, and
100 watts to each of 4 speakers is just about all anyone would ever need.

Also, make sure that you have more amp than speaker.
so if you go with the 75 x 4 amp, look for 50-60 watt speakers,

if you have more amp than speaker,
the speakers have all they need to sound as good as they can,
and you amp can keep its cool running at say 80 percent.

if there is not enough amp for the speakers,
there just isn't enough juice to run the speakers,
so you turn up the volume and the amp is running at 100 percent
trying to deliver the power that the speakers need,
and the speakers don't get the power they need to perform adequately,
result is blown speakers or worse yet, blown amp.
Don't be afraid to over power your speakers,
they'll take what they need, just don't underpower them.

As far as subs go seald box in the trunk seems to work the charm,
folow same powerring rules as above, and you're golden...