2012 non-JBL same as previous?

So Toyota has re-jiggered the different Prius levels this year, and now the III is looking more attractive than the IV (last year it was the other way, but I ended up postponing the purchase). Can anyone confirm if the amp and speakers situation in the non-JBL system in the 2012 is the same as it was in the past? I think I'm starting to get a handle on how I would upgrade the base audio system, but if the base system is hasn't changed in any significant way.

Tentative plan:
1) Keep head unit (don't feel like messing with it)
2) Add 4-channel class D amp (probably JL 400/4): two channels for fronts, two channels bridged for sub.
3) Replace squawkers with 3 1/2 coax, leave front 6x9's. Probably high-pass the fronts (in the amp) at 80 or 100 Hz.
4) Replace rear doors with 6 1/2 coax, drive off the head unit.
5) Add sub to trunk (details TBD, but I have a couple of options there).

This type of approach has served me well in the past, giving a huge sound upgrade with modest expenditure. Way cheaper than the spread between the III and IV now, certainly.

Anyone know for sure about the 2012 base system details?