Stock stereo wire Q's
 

Good morning. NOT new to cars/machinery, but new to Toyota's and their operational systems.

Vehicle: '02 is300, auto and P/O had installed a cheap Pioneer 2-din unit that only worked when IT wanted.
I purchased a Sony 1-din headunit and 'kit to install, and find out that the 'stock' wiring for the Antenna is Siamesed with two other wires.
One is the MICRO antenna, one has been snipped off, and the other is might be a ground.
It had crap reception and P/O installed a amplified antenna spliced in, and 3' of wire all wrapped up in a bundle.

Wanted to know if the STOCK antenna wire/cable can have an adapter or __ to plug into the Sony head unit?
What are these other two wires?

Yes, ordered another 'conversion' adapter/interface to be able to utilize the stock amp. So that should be taken care of.
Also, the speakers I have are 6.5's (2-way) for the front doors.And 2-way 6x9's for rear) BEFORE I found out that they were separates up front and
built in crossover for them and rears.
(what a PAIN just to install a dang radio..)

Saw some pics and read some write-ups on how to remove the pocket from behind the rear armrest for subs. But I thought of just removing the rear door pockets and installing two 6" subs in those using some masonite or MDF, but I'd have to find the wiring in the rockers for the rear speakers to tie into or run a separate woofer for them.

Thanks for any help/input.
E