It is a bit complicated.
The original audio series was quite tightly tied together with the book series, with the books becoming less and less important over time. By series 7-9, the audios had become the dominant storyline, so I don’t think you’ll encounter any problems there.
However, series 7-9 follow on quite significantly from series 2-6. Several characters, including really important ones like Jason and Brax, definitely require context from earlier stories IMO (and I’m usually in favour of jumping in at the deep end without any prerequisites).
However, lots of individual stories are quite standalone!
@ivqks159 has made a fantastic guide to the Benny series which I’ll link to here: