Reporting back. I ended up connecting Fire Tablet 8 via USB OTG cable to the Apple dongle instead. The sound quality is fine, but because Fire Tablet 8 only has one USB port, so whenever I am using the port for music, the tablet is not charging. I have to plug/unplug between the Apple dongle and the charging brick, which is annoying. Amazon sells USB OTG/charging splitters, but I don't think they work for Fire Tablets.
Edit: I forgot to mention that Apple dongle had low volume issue that required me to turn up the amplifier. I also tried the Google headphone dongle, which had normal volume, but not as high quality of sound. Combined with the charging issue mentioned above, Fire Tablet is overall not very satisfactory as a streamer.