Re: Let's put an XLR in a guitar!
What do you mean "outputs"? An XLR has three pins, and when used for a mic or a balanced connection, they're typically signal, inverse signal, and ground.
A standard 1/4" plug for guitar has two contacts: signal and ground.
So, if you went with an XLR you'd only be gaining one extra connection, not two like you think (you forgot about ground). You could also accomplish the same thing with a TRS 1/4" cable and you wouldn't have to route anything for the bigger XLR jack.
In any case, electric guitars with a piezo sometimes already use a TRS jack. This allows you to send the magnetic and piezo signals to different amps.
I don't know of any setup that allows for what you want to do though. Why do you need to record all three at the same time?