Guitar > GT-10 or X3-Live > amp preamp > GT-10 or X3-Live > amp power amp
The send receive in your GT-10 effects path should be AFTER your comp/distortion/amp sims and BEFORE your chorous/delay/reverb effects.
Note that you can still put external pedals in the right places - i.e. real wah pedal before the GT-10 input or a distortion stomp box before the amp input and other effects processors in the loop before/after the GT-10.
Here is a link for further description: http://www.benvesco.com/blog/pod-x3-live-tips-and-tricks/2008/pod-xt-x3-live-tips-and-tricks-four-cable-method/