Preamp voltage

When choosing a new HU what level of importance would you give to the preamp voltage level? I'm getting ready to change an older Clarion Pro Audio unit with either 4 or 5 volt preamp and wanted to know how much this should affect my decision in buying a new HU. The system consists of  RF 400a4, RF 800a2 amps, JL mids and highs, 3 JL 12W3v2-D6's.

I recently purchased the Kenwood KDC-MP4028 with 4 volt preamps for my second vehicle. It too replaced an older Clarion Pro Audio unit. It sounds beautiful, but this system is hardly the size of the previous mentioned one.  Both HU's have had F,R,S preamp outputs which I want again, and I also like the Kenwoods bulit in crossover system but I am not completely sold on Kenwood. I like the Apline HU's but only the highest priced ones have 4+ preamp voltage. Some lower priced Alpines have the F,R,S preamps but w/o the higher voltage. What do I do?

There are a couple of factors to consider here. 1. A higher output pre amp will combat noise better and improve signal strength. Also you will be able to lower the gains on your amp in order to have better head room.

2. A source no matter the voltage will only be as good as its point of origin. So a deck that claims 6volts on its pre outs may not sound as good as the deck with the 4 volt pre outs that has a cleaner signal to begin with.

3. Impedance is important as well, a lower impedance will be less affected than the higher impedance signal.

4. It can be difficult to match gains if the amps max sensitivity is below the pre amp level, for example my eclipse deck uses 8 volt pre outs and some amps can only accept 4 volt max in, so one must keep the gain very low.

And now for the "dummy" answer from me, king of dummies...

If the only difference between the 2 HU's is output voltage, go with the higher so long as your amps can handle it, which they should be fine with.  If there are other differences between the units, I'd ignore the output voltages & pick then one that I liked better - there's not going to be a discernable SQ/noise difference with that setup using either 4 or 5v outs.