FWIW: Sony's Digital8, a digital video format that used Hi8 video tape, did not come out until around 1999 so it is not likely the tapes are Digital8 video based on the reported age.
There is a digital audio format (DTRS) that used Hi8 video tape cartridges that came out in the early 1990s.
https://en.wikipedia.org/wiki/DA-88.
http://www.silentway.com/definitive-...rmat-recorders
It may have been used to make audio recordings in studio environments, but not in the 1980s.
Hi8 video recordings could have had a Hi-Fi Stereo audio that is roughly on a par with FM broadcast audio quality, and would fit in the reported time period.
Finding a Hi8 player (camcorder or VCR) would tell you if the tapes contain video. (Many Digital8 video players can play Video8/Hi8 as well.) Confirming DTRS format recording may be a bit more difficult.
Giving you location might be an aid in finding source of help close to you unless you prefer to do it via mail, in which a search of DTRS audio tape conversion might give some options such as:
https://www.deepsignalstudios.com/audio-transfers
(I know nothing about them)
But who ever you consider, call them first to sort out their abilities, costs, etc.