Thinking of adding a sub
 

I have a 2013 FRS 10 series with the touchscreen pioneer deck. I am thinking about adding a sub/amp combo just to add a little more bass and sound quality to the system. The door speakers are ok so I am not going to mess with them. I found this soundstream all in one unit and I was wondering if anyone has ever tried to mount one of these under the seat or behind the seat? Also how did the pioneer deck work out with adding an aftermarket sub and amp. I know the sound will not be ass good as a separate amp and sub but I am more less trying to do it so it saves space and when I sell the car I can just pull this out and go on about my day.

I'm not familiar with the Soundstream unit you are talking about, but keep in mind there is only 2" beneath the seats. So make sure to check the dimensions (most amps won't fit under the seat).

Your overthinking this way too much.
Any amp/sub combo will be 100x better, and would work great with any stock unit.
I would put my effort in choosing the right sub box. If you mean this bad boy [ame="http://www.amazon.com/Soundstream-USB-8A-Powered-Subwoofer-Enclosure/dp/B0085CAYZ6"]Amazon.com : Soundstream USB-8A 8-Inch Powered Subwoofer Slim Enclosure : Vehicle Subwoofers : Car Electronics[/ame] then it would sound just fine.

Your still going to need a wiring kit. But you can always leave that behind.

Yes sir that is the one. I got it for $100 shipped. I could always do it behind the driver seat as well. Do you know if the stock pioneer touchscreen deck has RCA jacks and if I need a line level converter?

I'm really not 100% sure the stock head unit has one, but you don't need a line converter. It already has one built in. Just incase you don't have RCA outputs.
I would read your manual just to double check if it has it.

I have a 10 series as well and had the impression that all FRS had rca jacks but pulled HU out today and no RCA so now im trying to research how to wire a soundstream st1.700d amp.

LC2i with the OEM male and female harnesses to get signal off the OEM amp.

http://www.ft86club.com/forums/showthread.php?t=42239

Or if that amp can take high level inputs just get the two harnesses and wire in your amp.

Thanks! Found that thread yesterday and it helped a lot. Im thinking of tapping into the stock amp to get signal. I want to keep the door speakers. My plan for mounting amp changes original plan was under seat to keep trunk clean. Now ima try to bolt to back of seat in trunk