The Italian video has credits lifted from another film at the start (a Danish film called Without a Stitch) but some possibly partly genuine credits at the end. It may be from the early 80s rather than the late 70s.
André Kay and his photographer friend (Chris Loussert) visit a woman (XNK0066) and have a threesome.
André's wife (Macha) is frustrated and goes to see some sort of therapist (Mme Candice, Voyante, Eva Muller) who shows her a porn video and seduces her. Two blondes (one is XNK0069) appear in this film within a film.
Mme Candice gets the wife to video herself and husband having sex. The therapist's lesbian lover (or previous client, XNK0544), after experimenting as a streetwalker, finds the film and takes pictures of the screen for blackmail purposes. André, two male friends (Chris Loussert and possibly Louiison Boutin) and André's wife go round and force the therapist and her lover into an orgy as punishment. The lover is DP'd.
Additional information from Skin Flick.