This is just an audio signal, not more complicated than recording a mic. So test if your line in is properly working (with a mic) and do the same with your line out by plugging headphones into your 3DS. We can't be really helpful just knowing that "sound doesn't record". Audio recording has...
Install BootNTRSelector-FONZD-Banner.cia. I never tried the other. Here is a QR code if you want to install the cia with the remote installer of FBI. Should works.
Exactly. NTR drops only when I begin streaming. I will try on my laptop. I can add that I upload via 4G and get 3DS video via my provider's box. So I don't think it's a problem due to an overloaded network.