Thanks for all your answers, guys.
From a Mac user point of view I can understand what RealZap means. I'd love to go with iTunes - if they had made it just a little simpler... So, to be frank, my way of thinking was just the other way around - why should I bother with an (in my eyes) very complicated system like iTunes which I never really got to work as I wanted it to and which - as far as i know - can only handle audio files I have either bought in the iTunes store or which have been ripped by this program? I have so many more mp3s that have been generated by 3rd party stuff and they're not considered by iTunes as part of its library, and synchronization will not include them... ?
So I thought there must be a better way for me... and, yes, after googling for about 30 minutes I found a little helper app called "copytrans" (installed it on my PC with Win 7) which allows to copy mp3s from my HDD directly onto the iPad via usb (and even into the right folder, as far as i can see).
Did this, created a playlist on the ipad and... hooray, the Amplifi remote app recognizes songs, albums and playlists. And the auto tone detection seems to be working, too! ;)