2009 touring Bose HU repalce but keep the Rest

[chirowolf]

My plan it to trade out my Bose Head Unit and replace it with a Pioneer AVIC Z120BT Head Unit with Navi.
I know all the audio experts say replace everything. truth be told I do not hear too well adn the extra bucks will be spent on other upgrades.

So this is what I have so far

PIONEER AVIC-Z120BT
Pioneer ND-BC20PA Universal Rearview Camera With Parking Assist Visual Display
Axxess mounting kit

Not sure which steering wheel control Axxess or PAC?
Which wiring harness?
I plan to keep the bose speaker and amp. Do I need to buy a preamp to get the Pioneer to play nice with the Bose?

Do I need this?
PAC SOEM-4 ADJUSTABLE LINE OUTPUT 4 CHANNEL CONVERTER

Anyone who has input please give your .02

Would also like to know if anyone knows any good install shops in the St.Louis area.
I could probably do the install myself, but not sure if I have the time.
I have read alot of the threads and gotten some usefull advice, but any additional gems would be great.