...it turns out the ADPCM decoding algorithm(OKI/Dialogic) I was using was slightly wrong(which caused a bit of extra noise and distortion in the decoded music than what should have been there).
NEC seems to have modified the delta step calculation algorithm in a subtle manner compared to the stock OKI algorithm(whether intentionally or if it was an accident, I don't know) for the PC-FX. If anyone's interested, I can release fixed copies of the music rippers.
I sure don't see a reason why you shouldn't! The more tools out there the better!
I second exodus - please release the fixed version of your ripper!
Der Langrisser FX music dumper updated(see the README file in the ZIP):
http://nekozomb.fobby.net/music/der-langrisser-fx/