Actually, out 3 & 4 are set up for outboard gear, pedals & 4cm & can achieve unity gain with the physical output knobs all the way up. They are not line level. Since this is a drive pedal, is it before or after the amp? If it's after, that could create a lot of noise.
From the manual:
TIP: OPTIMIZE FOR LOW NOISE
The optional Boost/Pad functions on Outputs 3 and 4 are designed to run the D/A converters at boosted levels, padding their outputs for even lower noise. To find the right setting, adjust either of these settings as high as possible without clipping the outputs, as indicated by a red LED on the front panel meters. You’ll actually hear the noise floor drop as you increase Boost/Pad. Find these options on the Audio page of the I/O menu under SETUP.
INSERTING OUTBOARD GEAR
Global Settings: As per your usual setup, check I/O Mono/Stereo SettingsPresets: Custom
With the typical “direct” setup using only Input 1 and Output 1, the Axe-Fx III has enough I/O blocks left over for multiple “send-and-return” inserts of outboard gear. The simple example below imagines a 3rd-party device inserted using Output 3 (used as a “send”) and Input 3 (used as a “return”). This setup can also be used with stereo inserts, or expanded with multiple I/O pairs for multiple outboard devices. Insert devices can even be added to other types of setups using these same techniques.
Custom presets are required for this type of setup, with output and input blocks added for the send and return points (see example below). The Axe-Fx III has no “FX LOOP” blocks, so inputs and outputs are placed individually on the grid. In a send/return pair, the Output block is connected to the Input block (as shown below), allowing the Input block (return) to serve as a master bypass control for the send/return loop.
CONNECTIONS
Connect your guitar to
Input 1 (Instrument).
This example assumes
Output 1 is connected to FRFR monitors.
- Connect Output 3 L as a “send” to the input of your outboard device. Adjust output levels using the front panel OUT 3 knob with the following considerations:Outputs 1 and 2 have options for –10 dbV and +4 dBu in SETUP: I/O: Audio.
- Outputs 3 and 4 provide unity gain when the knob is fully clockwise.
- You can also adjust the levels of an individual Output block.
Connect the output of your outboard device to
Input 3 L as a “return”. Adjust levels on your device or use the trim controls under
SETUP: I/O: Input.
Optionally connect the right channel inputs and outputs for stereo insert devices.