Adding an aftermarket Subwoofer. Please help!

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2013 Mazda 3 iTouring Hatchback
Hello everyone! This is the first time I've had a car newer than 10 years old, so I've never been a part of a car forum. So, thanks to anyone who responds to help me fix my issue.

The first thing I would like to specify is that I am leasing my car. Ive wanted a mazda3 hatchback for a LONG time, and i finally got one even though its just a lease. I have the 2013 Mazda 3 hatchback iTouring edition. Everything is stock.

In my last car, I had a sub-woofer and amp that worked amazingly together. I would have liked to have put the same set up in this car, but my amp is no longer working. I had my electrical engineer friend who works on computer boards for a living look at it, and he couldn't find the issue.

So my post breaks down into two questions. The first and most important, is how easy is it to install an aftermarket sub into a stock stereo system? The ideal set up would not change so much as to void my warranty and make me pay a bunch at the end of my lease. I was under the assumption that I could just tap into some wires with vampire clips or something and then just tape it all back up when I return the car and no one would be the wiser. If the process would require lots of irreversible alterations that will dock me in the end, then I will just turn back now. If not, then my first question is what would be the easiest way to do this.

My second question is what amp should I buy. The sub I have is a 12 inch infinity. Unfortunately I dont know anything else other than that. The box its in is all closed up and sealed. The amp i was using is the KAC-9103D. Heres the link:
http://www.crutchfield.com/S-DtVLpbOel1O/p_113KAC9103/Kenwood-KAC-9103D.html
It has since been discontinued, otherwise I would just buy it again. So my second question is what would be a good amp to replace the one I lost? I know that is hard to know without knowing what sub I have exactly, but hopefully knowing which amp I had before will help. As I said before, they worked wonderfully before and the technician that installed it was surprised at how good of a sound I got from the combination of the two.

Thanks again for whoever helps!
 
So I take it this forum is dead... All anyone is here to do is look at the new Enonon head unit. OK. Ill try elsewhere.
 
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