Ffmpeg, merging audio

Hello,

i have a question for you and a potecial order.
Iam working on a school project, where I need to do this and I am having these problems:

1) I am already using and playing with ffmpeg
2) The goal is to Merge (combine / mix) 2 or more tracks together.
3) So if I have one track with Guitar, and second track with drums.
After mixing the tracks you will hear the guitar with drums together (same function like audacity or other DAW)
4) The Mixing function works but
5) the problem is: after the mixing is done and sound is exported, one of the volume is decrased.
So I can hear guitar quite well with the same volume as the original single track. But the Drums are now much lower then the original track of drums.

6) I already tested, that function "normalise" don't work... The results are same
7) You can use -filter loudnorm 1.5 and incrase the volume of one track by 50%. But this is not the solution.

8) Iam looking for a command, that will solve this problem with merging audios.

Let me know if you know the solution and we can futher.

Thanks!!!
mark