04Pathfinder

Hello everyone, I recently bought a 2004 LE 4x4 from my parents. My father is very good with cars and always taking great care of their vehicles. It's got 64,000 miles and still in really great shape. I would greatly appreciate your collective knowledge on a few things for my truck. I recently plasti dipped the back embles and added a hitch frame. I plan on plasti dipping the rims and front grill as well. My biggest issue is the stereo, the sound isn't bad , it's just not great. The biggest thing it's lacking is an auxillary input. I've had one since I could drive! which is nearly 10 years. I want your opinions on the difficulty of installing new speakers with the amp issues or if I should just replace the head unit and get an adaptor to keep the stock speakers. Here is the unit I want, any idea how difficult it will be to install? I currently have the 6 disc bose stereo in the pathy. Unit I want http://www.amazon.com/gp/product/B00B8YTOZ4/ref=ox_sc_sfl_title_1?ie=UTF8&psc=1&smid=A1A9YNVFHZUZX0 Will this make it basically plug and play to use the stock speakers? http://www.amazon.com/gp/product/B000CE9OY2/ref=ox_sc_sfl_title_4?ie=UTF8&psc=1&smid=ATVPDKIKX0DER I would love to updgrade the speakers with some polks, but I'm not really interested in storing a large subwoofer in my ride. I'd ideally upgrade the speakers and have sufficient base with the high quality speakers. Can I use that adapter, keep the stock wiring and just replace the speakers as long as I'm using that apaptor ? Any input would be greatly appreciated. I really wanted the "missing link" but I gave them a call this morning and they no longer offer that item I'm going to go take some pics and up load them in a bit,

Just called and they no longer make it

I called about the missing link and was informed they no longer make it I would gladly buy one if we can get more people !