Whatever you do, don't record a post-amplification signal. The output is strong enough to damage recording equipment, all of which is designed to be used a pre-amplification levels.
Does the mixer have an Auxilary output, a monitor send, or perhaps a tape output? Any of these should work well enough for what you're trying to do. Actually the monitor send is a great way to do it, because you can adjust the levels of each instrument as they go to the recorder seperately from the main mix. Typically a recording from a direct output will result in an recording where the levels of the instruments are all wrong. This is understandable given they were set to sound good live.
In other words, if a direct recording from say a tape-out results in vocals being too loud for example, you won't be able to turn them down on the recording unless you also turn them down live. Using the monitor send solves this problem because you can soften the vocals t the recorder without having to turn them down in the live PA. Make sense?
