That did it!
Thank you very much thannoy & Rémi for helpful feedback!
For completion let me state what in the end worked on my system:
post recording conversion to mp3:
C:\Program files\VideoLAN\VLC\vlc.exe C:\test.mpg :sout=#transcode{acodec=mp3,ab=192,channels=2}:duplicate{dst=std{access=file,mux=raw,dst="C:\test.mp3"}} --no-sout-video
Direct DVB-T recording to mp3:
C:\Program files\VideoLAN\VLC\vlc.exe dvb-t:// :dvb-frequency=522000000 :dvb-bandwidth=-1 :program=3010 :sout=#transcode{acodec=mp3,ab=192,channels=2}:duplicate{dst=std{access=file,mux=raw,dst="C:\test.mp3"}} --no-sout-video
(aenc & samplerate weren't necessary, at least not for my test cases)