And for the Yamaha P3500s I am unsure about PreAmp specs. The voltage output, output impedence???!!!.
The Yamaha P3500s has 30Kohm balanced Input impedance, so as for the PreAmp would require to have anything less than 3Kohm, am I correct on that?. As far as the input voltage goes, I couldnt find any for the P3500.
A 1:10 ratio for impedance is ideal, of course. As for voltage, a balanced XLR output is supposed to have several times the voltage output of a consumer RCA output, and as a result, a device like the Yamaha amp expects that higher voltage; it's input stage was designed with this in mind. If you connect a regular consumer device to it's input, you would likely have to turn the gains up high on the Yamaha, causing possible noise/hiss.
Any suggestions on the PreAmp best suitable for the Yamaha P3500s?
The Adcom GFP750 has balanced outputs and is considered a very high quality device. This is just one example. You'll have to look these up. I think Parasound has some balanced output pre-amps as well.
BTW, if you ever intend on using subwoofers on your system, then you can avoid having to use a balanced output pre-amp by using a DCX2496 by Behringer. This is a sophisticated DSP xover and EQ system. It would be used by connecting the pre-amp output to the DCX input and then sending a pair of DCX outputs to your main speaker amp and then another pair of DCX output to the subwoofers. This DCX will allow ideal integration of the mains/subs for seamless response, and in addition, allow room correction and allow custom modification of the signal to get the specific bass signature that you desire, as well as acting as a precision filter to customize your main channel response. The DCX has balanced inputs, but it's input pre-amp was specifically designed to also take consumer unbalanced voltages and boost them for internal use of the DCX, so you can use a simple direct RCA to XLR adapter and feed the DCX inputs, and then feed the balanced DCX outputs to the amplifier(s).
BTW, the Yamaha amps have rack mount wings. Some people find these annoying, as they don't look right mixed with other gear in the system. But, be aware, these wings come off. A few screws hold them on and they are easily removed.
-Chris