Can you explain to me how one would send a pre-recorded guitar track (for example) to an amp? Does one need a re-amping device to do that? Also what does line level mean?
One records one guitar through two amps at the same time with a splitter of some sort. Are there any splitters you can recommend?
Yes, to send a pre-recorded guitar track to an amp, you need some sort of reamp device. This is because your audio outputs on your soundcard, or digital mixer, or D/A converters (whatever you use to get your sound out of your computer) will be at "line level", whereas the input to your guitar amp is expecting an "instrument level" signal. Without getting into all the technical details, line level is a MUCH hotter (louder, higher voltage, etc.) signal than the output of a guitar, and the impedances are different as well. This will overload the input to your guitar amp, and the impedance mismatch will also screw up the sound.
To further complicate things, there are two different "line levels" for equipment. There is the consumer line level, which usually appears on unbalanced connectors (such as the RCA type phono plugs found on most stereo equipment, or simple 1/4" unbalanced connectors for home targeted recording equipment), and is specified as a level of -10dBV. On the professional side, you usually have balanced connections (using three connector systems, such as XLR, or TRS type 1/4" connectors), and they have a specified level of +4dBV. So, even mixing and matching different line level type connections can be a problem if they aren't the same spec (consumer or pro). For example, most synths and keyboards have 1/4" outputs at the consumer -10 level, while professional mixing boards have +4 line level inputs... so, there is a mismatch right there, and many times the pros use direct boxes in the studio to interface the outputs of keyboards and synths with microphone pre-amps whose output can then be at the correct +4 line level for the console or tape deck inputs.
To read up more on line level, check out the wikipedia entry:
Yes, if you want to have one guitar going through more than one amp at the same time, you'll need a splitter designed for that. I'm not a guitar player, and haven't ever actually recorded a setup with a guitar feeding more than one amp at a time, so I don't have any recommendations from personal experience. However, most people highly recommend anything from Radial Engineering. I have one of their DI boxes which is built like a tank and sounds great. They've got re-amp boxes, splitters, distributors, DI boxes, and several combination devices as well.