The Rockford system is OK, just not terribly good as auto audio goes. Have had two Titans with Rockford, replaced HUs in both.
As stated above: simpliest solution, if in fact speakers are blown, just replace the speakers. They are 2 ohm impedance.
Backup camera will work with new HU. There is an adapter cable available from AXXESS that makes it plug and play (used one on my '13 Titan). Be advised that you lose the 'grid lines' when doing this. Also, the OEM camera is supplied 6vdc by the the Nissan HU, the AXXESS adapter applies 12vdc - had no problem using the AXXESS cable on my 13 Titan. However, if you are nervous about using the AXXESS cable as is you can add a 12v to 6v converter IC (about $2.00 at Fry's or similar) to the wiring. I did this on my presently owned 2016 Frontier.
As stated above: simpliest solution, if in fact speakers are blown, just replace the speakers. They are 2 ohm impedance.
Backup camera will work with new HU. There is an adapter cable available from AXXESS that makes it plug and play (used one on my '13 Titan). Be advised that you lose the 'grid lines' when doing this. Also, the OEM camera is supplied 6vdc by the the Nissan HU, the AXXESS adapter applies 12vdc - had no problem using the AXXESS cable on my 13 Titan. However, if you are nervous about using the AXXESS cable as is you can add a 12v to 6v converter IC (about $2.00 at Fry's or similar) to the wiring. I did this on my presently owned 2016 Frontier.