The "Extra Quality" aspect typically refers to the enhanced production values and specialized audio triggers used to maximize immersion:
Use of lossless audio formats (like FLAC or high-bitrate MP3) to ensure every subtle whisper or rustle is captured. nemuru koneko suimin no machi rj01062044 extra quality
(This is a unique identifier typically used on DLsite, a major Japanese digital marketplace for doujin works). The "Extra Quality" aspect typically refers to the