Surprisingly, those two options didn’t work, however I was able to find an mp3 converter online with volume increase+ reduction options:
https://www.onlineconverter.com/increase-mp3-volume
I had to reduce the mp3 from Garageband down to 90% of its original volume, then take that new mp3 and lower again to around 50% to get a usable level with the 1440 at full volume. The playback quality is good as well.
Ultimately not too tricky and it worked out in the end.
