cobaltss4u2env06

i feel like ive been running around trying to find out what i need to run a aftermarket headunit. i want to run a pioneer 4100 in dash. so i understand that i need the metra double din (http://cgi.ebay.com/CHEVROLET-COBALT...item53dcc60f3d) and i also need the antenna adapter (http://cgi.ebay.com/GM6-GM-CHEVY-ANT...item20adaea84b) but i have heard that i need the pac swi-ps. but when i call up best but they say i should use the scosche gm13sr because that includes the metra wiring harness. when you buy the pac swi, you have to buy a seperate wiring harness(http://cgi.ebay.com/CHEVY-MALIBU-PON...item5187cca55b) out of all this, what do i really need?

Dash kit, pac swi-ps, metra 70-2013, antenna adapter. or should i use the scosche gm13sr which eliminates the 70-2013 wiring harness?