GT-1000 can run a Wet/Dry setup over both mono and stereo L/R outputs.
There are blocks in the effect chain of the GT-1000 called DIVIDER.
When you adjust the DIVIDER from SINGLE to DUAL, this splits the input signal between two parallel paths. All effect blocks are moveable in the GT-1000, so any number of effects and amps can be put into a dry or wet path of your choosing. When using the onboard GT-1000 UI, to move an effect block around in the effect chain, highlight the effect block, then push and turn simultaneously on KNOB 6 to move the effect block in the effect chain.
WET/DRY IN MONO SCENARIO
In a mono setup you can change the DIVIDER to DUAL, This will give you a dedicated WET and DRY path in parallel mono.
Highlight any of the effects block, Press and simultaneously turn [6] KNOB/BUTTON to move effect blocks into your desired wet path.
There is a second page of controls for the DIVIDER section, this will give you level controls and ratio controls for both sides of the DIVIDER.
WET/DRY IN TRUE STEREO SCENARIO
Highlight the speaker icon labeled M L/R, turn [1] KNOB/BUTTON to turn off stereo link.
Now, both Left and Right 1/4" TS output jacks are separated.
Press and turn simultaneously on [6] knob to move speaker icon M L and speaker icon M R to either the DRY or WET paths.
DISCLAIMER: Be sure to attempt this type of set up at a low volume before attempting performance. Overload is possible, if not careful about the output signal, when the DIVIDER is engaged. 
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Our GT-1000 Ultimate Guide Video Series is a great resource for users that are visual learners.
GT-1000 ULTIMATE GUIDE VIDEO SERIES