It is also not 100% clear for myself.
I am not sure that I understand the all thing precisely, and I could not find information on the manual.
That said, I made some experiment , and I can deliver you the results of my own trials.
I have tried to put a homemade clone of SDD3000 preamp into the loop of my Axe FX.
Basically, there is three parameters.
Output 2 => send level to your pedal ;
Input 2 => return level after your pedal entering the Axe FX II.
FX loop bloc level ; level of the bloc send to the rest of the chain after the block Loop (about the same effect as the amp level parameter on amp bloc)
In my case, I decided to set the volume on my pedal knob at 11'o'clock, because this is the position I have used in the past with a real amp. (I needed something to start with !)
Then, as I know that this pedal can boost about 30db, I have set the level in my FXloop block to -20 db (am I right or totally wrong doing so ????)
Then I put output 2 (front panel knob ) at about 70% (is it the optimal value ?)
Finally, I tweaked the Input 1 in Axe FX I/O until the red light slightly comes when playing hard. (This is about the same procedure as setting the input for your instrument). It is of course important not to clip the all thing.
At the end I have something which sounds good, and Preset level is at about 0 Db with VU meter.
You have here the all details of my trials if it can help you. (I have compared to the FET preamp model in Axe FX , so both version sounds about identical at the same volume)
I have reach a result that I like, but I am not sure at all that this is the best configuration.
Preset
http://axechange.fractalaudio.com/detail.php?preset=5919
(Preset with pedal in loop sounds identical to preset with FET preamp model )
The result with the pedal into the loop
I hope it could help you !
Axe FX II loop /
DIY pedal SDD3000 preamp without attenuators ; identical to Dirk Hendrick model without attenuators.
A video not from me just to show you about the pedal I have tested)
Pedal in the loop, volume/gain 11 0'clock on the pedal (just one knob on my pedal).
FX loop block after drive and before amp bloc.
I/O page AXE FX II
Input 2 65% (this is the FX return of the loop)
Instr in 92% (Stratocaster)
Audio
Input 2 left only
Output 2 mode stereo
Output 2 boost/pad 0 db
Output 2 phase normal
Output 2 echo normal
Output 2 level (front panel) 71%
Block FXloop
Level -20db
Bypass thru
----------------
ALL AXE FX II (no pedal in loop)
Block FET preamp (drive) (to simulate the SDD3000 pedal)
after drive 2 and before Amp block
Basic
Drive 4.5
Tone 4.5
Input select L+R
Advanced
Low cut 20 HZ
High cut 9000 Hz
Clip type FET
Bass -6db
Middle freq 650 Hz
Mid +2 db
Treble 0db
Mixer
Mix 100%
Level 3.2
Balance 0
Bypass mode thru