On another forum I frequent, somebody wanted to use an LS-2 to act as a mixer for two guitars - so similar as acting as a mixer for the two outputs. However, while this is possible, somebody who had tried it said that the LS-2 was far too noisy for this application.

I haven't got one so can't comment, but if you already have one, it's worth trying to see what the noise level is like when you've got two guitars plugged into the two return sockets (not the main input). In the A+B Mix/Bypass mode setting, you can input two signals via the A and B return sockets and mix them using the two level control knobs. When in bypass, you won't hear anything from those two inputs but will hear whatever's plugged into the LS-2's main input. If that's likely to be nothing, it may be well to make up a jack plug with the tip and sleeve shorted so that you get silence (rather than the noise picked and hum up by an open cable), so the LS-2 acts as a mute switch when in bypass.

If it sounds like it's adding a lot of noise, then you may be better off running through a passive mixer.