Only a non-answer for now:
I searched on this issue for weeks, and found no research or publication that investigate what Ayasugi or other sound box patterning actually do (in English at least). In some translations from Japanese or Chinese, it is simply stated that this feature improves the sound. I searched mostly for the instruments Koto and Gu-Qin.
If it is only for personal use, then you should be fine. If you are thinking of any commercial application, you need to be au-fait with the licensing restrictions around any audio you access and use. This will differ depending on the audio source and you need to be very clear on what these licenses allow you to do.