Truck: 2004 Xterra w/ OEM Rockford Fosgate 6 disk changer, amp, & sub.

Reader’s Digest Version:
What is the ‘preamp’ voltage output of the stock Rockford Fosgate head unit / input voltage sensitivity range of the stock RF amp?

Longer version:
I have read every post on multiple forums related to installing an aftermarket head unit with the factory RF amp to no avail. I have found a number of posts stating that the stock RF amp ‘prefers’ higher input voltages from the preamps of a head unit. But, no one has stated what the higher voltage values are that it prefers. I did however find a post stating one user was having less then optimal output from his 2V preamps. I have been shopping around for a new source unit and have found one that fits my needs perfectly, but its maximum output voltage is 7V RMS. With most units I have come across having output voltages between 2V and 4.5V, the 7V max output made me hesitate since I certainly don't want to fry the amp, making my cheap & simple fix into a much more expensive proposition.

So does anyone know what the RF amp’s input voltage range is for each channel?

Or is there a way I can just measure it with my multimeter without hacking up the wiring harness?

Also, in the Nissan service manual on page AV-16 there is a table of “Audio Unit Voltages”, with a list of terminal #s 1-16, wire colors, and voltages for the premium audio system. The terminal #s match up to the wiring diagram of the head unit & amp on page AV-11 & the listed voltages make some sense with what they are labeled as on the diagram (i.e. Inputs for Front & Rear/ Right & Left speakers are all listed as 5V-7.5V, while the ignition switch and battery inputs to the HU are listed as 10.8V-15.6V). But what has me concerned about this table is that the wire colors listed refer only to the diagram of the non-RF system without the stock amplifier. Can I still be confident that this table applies to my Rockford HU and amp since it lists the ‘Premium Audio System’ separately from the ‘Base Audio System’?

Any input on the topic will be greatly appreciated.