By the way, the preamp is called the "K-5xe", while the power amp is the "V-5xe". I know, it's confusing...
As far as the gain goes, the normal gain structure is just right for most systems. The nominal output of a CD player is 2 volts, but most players will put out more than this.
Most power amps will clip with less than 2 volts input. (The standard gain for a power amp is 26 dB = 20x, so 2 volts would clip a 200 watt power amp with standard gain.) So you really don't need *any* gain for most situations.
But it is nice to have some gain in reserve to account for oddball situations. So 4 dB single-ended and 10 dB balanced has turned out to be a great all-around compromise. I don't think we've had a single complaint.
But if for some reason it doesn't work with your particular system, there is a single resistor per channel that sets the gain of the K-5xe. It can be changed with a screwdriver (no soldering), so this is something you can do yourself. I doubt you will need to. If you need to change the gain, just call the factory (Michael at x223) and we will send different resistors at no charge.