James I'm not sure if I'm understanding your post correctly since English does not seem to be your first language, but the audio from Akumajou Densetsu while playing the actual cart is the same volume as any other game. It's only quieter when you're playing it with the N8.
BTW Krikzz, I'm happy that you've made some progress with the FDS audio, but it still has pitch issues. I'm aware that the FDS audio is inherently ever so slightly out of tune compared to the regular Famicom audio in a real FDS setup, but when you play VS Excitebike, for example, you'll begin to notice that the higher the note, the more out of tune it is. It's like for every incrementally higher note, the pitch issue gets increasingly worse. It's not how the FDS audio actually behaves at all.
I'll probably just end up getting a FDS Stick haha.