BTR5 case in a similar form factor as the original supplied by Fiio.
The easy print version is designed to limit supports, and is printable using only supports from build platform, as shown in images.
No clip versions are if adhesive mounting or supplying your own clip.
This design should be fine with most print settings and most non-flex filaments. Prints in photos are 0.5mm nozzle, 0.28mm layers in PETG, but the standard 0.4mm nozzle and 0.2mm layers with PLA are likely fine too.
As the case depends on a fairly tight fit due to the rather odd shape of the BTR5, some post processing may be needed to remove droopy overhands or seams if present and to smooth areas that could be in contact with skin.
F3d files included have Parameters to easily change case shell thickness, clip thickness and the tolerance offset from the BTR5. This is so that the clip stiffness and case fitment stiffness can be adjusted for different filaments or to taste.
I could not find a BTR5 model elsewhere on the internet, so have included the model I made here for others to use for their own design.
The author hasn't provided the model origin yet.