Friend of mine runs a GT6 with either a Triaxis or an Engl SE Pre, and there´s no loss in gain....
So, let´s go through the hook-up chain step by step:
- Guitar to GT6 Input
- GT6 Send (Insert) to MP1 Input
- MP1 Loop Send to GT6 Loop Return
- GT6 Output to MP1 Loop Return
- MP1 Output to Poweramp
(substitute GT6 for GX700 or GT5)
To match all the (input) gain levels, there´s some steps as well.
First, you have to set the MP-1 OD1 (T2) Trimpot to work at its optimum setting (for your needs). So here´s how:
(all taken from the
MP-1 Stock Gain Mod instructions; Step10)
Step 10: Tweaking the OD1 Trimpot
Here is how to set the input stage gain-trim:
1) Plug your MP-1 back into your rack, make sure you have ample access to the top of the unit.
2) Locate the OD1 Trimpot
3) Dial-up your favorite high-gain patch.
4) Grab your main axe, plug it in, and switch to your bridge pickup.
5) Set the OD1 Level Control to 5.0 or 6.0 (or 7.0 depending on your pickups). You will have to play around with this setting until you are happy with how the other channels sound, especially the Clean- Tube channel. I wouldn’t let this setting get above 8.0, it may get too muddy or noisy.
6) While you are doing palm mutes and/or heavy open chords (“Pull Me Under” is a good riff to test with BTW), have your little brother turn the trimpot dial with a little miniature screwdriver until the OD1 Clipping LED lights up frequently on downstrokes, but doesn't stay lit all the time.
Now when you´ve done that, you have to set the Boss Unit´s Send/Insert Level to match the MP1 input. I know that there´s a tiny knob on the back of the GX700 for that purpose. The GT6 should have something similar (or some way to "define" if the loop send/insert is line or instrument level).
Once you´ve found that knob/switch/setting, turn that knob/parameter to achieve the same results as you did with the T2 Trimpot as described above.
That should get you in the right direction