@bean
Yep, I moved all plug-ins except the three you mentioned in the "Disabled Plugins" drawer. No difference - I still have gaps and "stuttering" while playback with the newer MP3Cast plugins. Switching back to the 1.14 cures the problem - playback is smooth with no hearable problems.
The sound from the newer 1.19 plugin is clearer and more "crispier" - which is really nice - but sadly somewhat unusable for me at the moment.
BTW: My CPUDocky shows an avarage of 6% for the 1.14 plugin while playback - the 1.19 shows ~25% CPU usage. Is my machine too weak?