I am going to upgrade my 2010 SR5 bottom barrel system, but I want to keep the OEM head unit. I had planned on upgrading the eight speakers (partial to the Kicker KS series myself) and add an Alpine line driver to add about 40w per channel. I have read the Kappa 3.5" dash thread, all 27 pages, to get an idea of what has been done by other T4Rers. I what an unbelievable difference! - kappa 3.5 dash speakers

I came across this Toyota-specific product that is that I will be adding to my upgrade. It is called the ReCurve EZQ. It is a connects to OEM Toyota head unit, non nav/non JBL Nav non JBL and JBL w/ Nav (2005 - present for 4Runners) and it allows for plug n play after market amp(s) addition. The site is Taco Tunes, they started out as a Tacoma mod spot... ReCurve EZQ - Add amps to your stock Toyota Stereo (Head uni) Entune

Check it out, I hope this helps.

I am still hopeful that OEM Audio+ comes out with a system for the 5th gen. I mean they did build one for the FJ.

Just so you know, the 3.5 kicker ks fits in the fronts. I like them better than the Kappa. I also have the alpine in line driver/amp. It definitely improves sound to a satisfying level. I did swap my HU but that was not because I thought it was a must, I just didn't care for the stock one.