Hi anvious, please dont apologies for being 'completely noob' as you your questions are perfectly sensible and reasonable. I had to ask them once too.
The whole point of the separate PSU is so that manufacturers acb avoid the build costs of puttiing different PSUs in each piece of kit. Take laptops for example, they always come with PSUs so that Dell can sell the same PC all over the world. It also means you can take your Dell all over the world so long as you have have suitable plug adaptors. So long as the PSU outputs 24V AC at 500mA to the X-CAN, it will be what the amp needs. Bear in mind AC to AC PSUs are not the same as, or as common as AC to DC PSUs. If you can by from an official dealer then you can ensure you get a PSU suitable for where you are. If you ever move you may need to change the PSU.
You are right, power amps are for speakers and the V8P can be a preamp controlling volume and driving headphones.
The other nice feature we have not mentioned is the USB DAC within the amp. It can be connected to a PC with an A to B USB cable and you can listen to music off the computer. Others disagree, but I say the sound from the X-CANS DAC is very good. It is the same USB DAC chip that is in the MF V-DAC and V8DAC, so it cant be bad.