Preamp out voltage for 2005 Mountaineer

I am in the process of selecting a replacement stereo for my 2005 Mountaineer. I am intending to use the new stereo to drive the factory amplifiers. I know that there are several options ranging anywhere from 1V to 5V for the preamp outputs for the various stereos I am looking at. The prices for the stereos seems to go up as the voltage for the preamp goes up. Since there is little to no other differences other than the voltage I was hoping that someone could verify for me what the optimal voltage would be to dive the factory amplifiers.

Hold on a second,
2005s have the amp built into the radio.. The only external amp would be for the subwoofer.

Is that correct? God I hope so. That would make things so much easier.

Still need to know what the sub woofer amp is expecting though. Still, I could just replace the sub amp at some point in the future if my choice under-powers it.

The radio has a built in amp. Yes.

The subwoofer uses a crappy separate amp, that amp doesn't use RCA in, it just uses standard speaker wire in.

Get any radio that you like, don't worry about pre amp voltage. You shouldn't need to worry about that unless you're going to run a high quality 4 channel amp with great speakers. Lol.

Fun Fact: 97 was the last year that the speaker amp was external.