Have a look at cdt drivers and mosconi and jl audio amps ...
I'm kinda big into car audio , and I'm currently fitting out Debbie's beetle with a system .
The cdt 6.5" comps have had great success with in the past .
They can hit pretty low and In a stock boxster with the roof up I'd say you can go without a sub and get great sq .
At speed , with the roof down , and aftermarket exhaust , you may need some help with the bass ...
I have no idea on this .
The mosconi amp I am using for he front two channels is a neat amp with a TINY footprint . Should be ideal in a boxster .
Likewise the jl mono amp running the bass .
I normally fit the front stage first and tune that without a sub .
Depending on the install and system fitted you may not even need a sub depending on the type of music you listen to .
I never planned on fitting a sub into her beetle as I know the cdt comps I was fitting would be more than adequate for the type of music she listens to ( rock and punk) and the levels she listens at ( pretty damn loud) , but then I got a stocking deal on a top of the line cdt sq sub , so I decided it was too good to pass up and ordered it from them
I'll post a link to a thread I have somewhere online where I am making the carbon fibre sub enclosure if you like ?
My advice to you is :
Forget about the idea of coax speakers in the door ..
A good install can make cheaper gear sound good and a bad install can make expensive gear sound bad ... Budget for isolation , fabrication , and sound deadening . It makes a HUGE difference
And go join a car audio forum .
And go listen to a few local guys systems .
There are basically two types of car audio ..
SQ = sound quality ( like a good home hifi system)
SPL = sound pressure level ( like a niteklub system)
BUT ....... SQ doesnt need to be quiet
Go listen to a few installs and make sure you know exactly what you want , then ask the guys for ideas .
Most ice guys are just like car guys and will love you help you out
