Issue Recording Vocals PT12/MBox Pro 3 Input 03 (rear panel) - Works with input 01

[lnc77]

Hi everyone,

I am quite new with PT.

Problem:
When I use a mic plugged in input 03 on rear panel of my MBox Pro 3rd gen (Mic/Line 03 toggle buttom out i.e. for Mic to be active and Front/Rear toggle button 01 pushed to activate Rear inputs) I can hear vocals through the speakers (direct signal from Mic to MBox to Speakers) -BUT- when I try to record on a mono audio track in Pro Tools there is strictly no signal recorded (Track recording activated and Record button On). In the mix window I cannot see any input signal for the audio track. There is no signal going from MBox input 03 to PT via my Mac OS.

Note:
- I can record vocals in PT via a Mic plugged in input 01 on front panel (XLR-Jack cable). No issue. Signal goes from Mic to MBox to PT via Mac OS
And,
- I tried to record vocals in AUDACITY. Works fine using Mic in input 01 on front panel, but as for PT, does not work at all when Mic plugged in input 03 (rear panel XLR-XLR cable).

Analyse of the problem:
Looks like there is something wrong with Audio MIDI setup of my system because the issue is the same for Pro Tools and AUDACITY when trying to record via input 03 of the MBox.

Question:
Does anyone understand what’s happening here?
Can anyone help me?
Thanks in advance for the time you spend to answer.

Hereafter my setups:

Pro Tools setup:
Hardware setup: Aggregate E/S Pro Tools
Playback Engine: Aggregate E/S Pro Tools
E/S : Input 1-2 (integrated) / Stéréo / Analog 1L 2R / Input (integrated) 1 Mono M et Input (integrated) 2 Mono M - Output / Stéréo / Analog 1L 2R
But there is no other input and output possible. In other words on audio track own PT I can only choose from E/S given above (see attachements. Be aware: Being french I have the french version of PT, Entree = input, Sortie = Output)

Computer, OS & Material/Software setup:
iMac 24 inc Early 2009, Processor 3,06 GHz Intel Core 2 Duo, RAM 8Go 1067 MHz DDR3, Graphics NVIDIA GeForce GT 130 512 Mo.
OS X El Capitan Version 10.11.3
MBox Pro 3rd Gen / Firmware 1.0.4 (latest, but my computer is not certified by Avid. Too old)
Pro Tools 12 version 12.4.0