To answer question #1: a basic 3.5 mm stereo splitter will work fine. The only thing that might be annoying, depending on your OS and your amp, is the fact that you'll have to constantly fiddle with 2 different volume controls. For instance, you might have to crank up the volume out to your computer speakers to make them audible, but the same volume going to your amp could rumble the house--so you then have to either turn down the computer volume, or turn down the amp. There are a few possible workarounds for this problem, though:
- Some amps save a separate volume for each input.
- Windows Vista (and probably Windows 7) has independent volume controls for each app. If you have Vista or Win7, you can just use a different music player when you want to play music through your stereo system.
- You can also get 3.5mm stereo splitters with independent volume controls on the outputs, such as the Griffin SmartShare.
If you get a lot of hiss using a stereo splitter, you might want to turn down the volume on your computer and let your large amp do the work. The integrated amps on sound cards are sometimes very noisy.
Last, this may be obvious, but does your computer have a digital audio output? A lot of computers now have either a coax digital out (looks like a back or orange RCA connector), or an optical digital out. My desktop has both, and even my 6-year-old laptop came with an adapter cable that gives me coax digital audio output (as well as composite video and S-video). If you can hook the digital audio output up to your stereo equipment, you won't have to buy a splitter, and the audio quality won't be affected by the integrated sound card's amp.
As for question 2, you'll just need a cable with a 3.5mm headphone plug on one end and whatever your amp takes on the other end--either bare wires, banana plugs, or RCA plugs. If you need one with bare wires, I'd just go to Radio Shack or a similar store and buy the 3.5mm headphone connector, then solder it to some speaker wire.
To answer question 3: on the amp side, you probably want to plug into the AUX input. On the PC side, you would plug the 3.5mm splitter into your sound card's speaker port (usually color-coded green), then plug the speakers and amp into the splitter. Of course, if you have digital audio out on your computer and digital audio in on your stereo system, you would just connect those instead of using a 3.5mm splitter.