Just my 2 cents, but you would be way better off with replacing the deck, factory speakers and adding a sub. My AVIC touch screen has died 3 times so far and Pioneer charges 200 bucks/repair and only covers it for 30 days!!
I would highly recommend the Kenwood over Pioneer. It does it all and is more reliable from my experience. The Alpine PDX-5 is a great amp and fits perfect in the trunk. The mono channel will only push an efficient sub. Not good enough for my Alpine R-series 10" sub.

 

150 series terminal 20 - 18 Ga from clipsandfasteners.com (part no. 15498 au-ve-co pdkts)

 

It's down that hole on the left...

 

If you're taking a minimalist approach, IMO the dash spreakers and the sub make a big difference.

 

Thanks, much appreciated.

 

i just rewired my 01tt. new kenwood nav headunit and an alpine pdx-5. i t-tapped the speaker input into the oe amp plug and ran my own wires. i have the 6 speaker sound system non bose. i ran the 2 front and 2 rears to the 4 channels on the pdx-5 and wired the 2 door subs (i use that term loosely) in series and plugged them into the 5th sub channel on the amp. after some fiddling with the gain and eq, i have to admit it does sound pretty damn good. im no audiophile but this is waay better than stock. definitely worth it!