NI A6 - TR-8: Audio Signals (Input) are really quiet in mono

[TechnoLover]

Hi everyone,

Here is my configuration :
- Ableton 9
- Mac OS X El Capitan
- Native Instruments Audio 6 (USB)
- Roland TR-8 (USB)
- A few midi controllers (Push, Akai APC40 and Akai MPK49)

I was using my TR-8 on Ableton (through USB) using an "Aggregate Device" that I created on OS X (made with the iMac Integrated Sound Card and the TR-8) to be able to use several audio interfaces together and everything was working perfectly (every channel was routed as "Mono Channels").

I decided to plug my Native Instruments Audio 6 and created a new Aggregate Device for the A6 and the TR-8. (I am pretty sure the problem doesn't come from the aggregate device as I face the same problem when using the TR-8 as input)

That's where comes the problem : all the "mono channels" are really quiet, that's almost impossible to hear anything. If I only activate the stereo channels, everything is OK. (but It's not what I want as all channels are grouped by 2 and I wanna be able to work with all my TR-8 channels as separated channels)

Something even weirder : The audio signals seem to be perfectly normal as their levels are as high as they are in stereo. (as example, the meter of the kick channel goes red which should mean it's working correctly but it's quiet as hell)

I noticed the sound is pretty quiet on :
- Audio channels coming external devices as the TR-8
- Midi channels using VSTs

I tried to use the "utility tip" and added an effect rack on a stereo channel (the channel 3/4 with the KICK and the SNARE) and put one utility in left mode on a chain called "KICK" and on second chain called "SNARE" to be able to separate the signals but both chains are really quiet too.

If I play a audio loop or a sample, the sound is OK. If I play some melodies on a VST, it's quiet.

Your help is highly welcome because I feel totally lost about this.. I tried almost everything I found on the internet but that doesn't help.

Thanks !

[TechnoLover]

SOLVED : I am really ashamed ... The problem was the master output. I am only using one speaker right now as I am lacking of cables and I the master output was "1/2" ... I just put to 1 (or even 2) and the sound is now OK.

Sorry for disturbing you guys