is there a big difference in the sound performance between the Pre Output Voltage if one unit have 2V and other 5V? Like the DDX7015 and the DDX7017, I can save like 200-300dlls because that is the main difference. does it really matter?

 

There is a big difference between 2V and 5V, but here's what you need to consider... 2 volts won't give you any improvement in sound quality over 5V. However If there is any noise induced into your RCA's, then the 5V will sound better.

Example: Any given amplifier has a gain of 100... with a max output of 400 units

2V signal, 1.5volts noise... 2X100 and 1.5x100 200/150 units
5V signal, 1.5volts noise... 5x100 and 1.5x100 500/150 units (see we're clipping here, so gain must be turned down to 80)

5v signal, 1.5volts noise... 5x80 and 1.5x 80 400/120 units

The ratio of signal to noise is less with the greater voltage input. But the gains on the amp must be proportionatly reduced... It's a give/take sort of thing.

Having a 5V input will not (always) give you a louder system due to the fact that you will also have to lower the gain on your amplifier to keep it from clipping at higher volumes

I'm trying to keep this simple (avoiding SWR and max power transfer stuff), hope this makes sense...