Can a man listen to a woman give a shiur (Torah class)? Does it matter if it's not in a class format — like, let's say it's on a CD?
Per Rabbi Avraham Yosef it is permitted 100% to listen to a recording of a woman giving a Shiur. However it is prohibited to sit at a Shiur which is being given by a woman.
I cannot tell from your question if you're concern is focused on Kol Isha. I am assuming that is the focus. This article discusses Kol Isha and when and how it applies, citing various viewpoints. I am citing one of the permissible views. Read the remaining sections of the article, as there are varying opinions.
Rabbi Yehiel Yaakov Weinberg (Seridei Esh 2:8) defended the German-Jewish custom of mixed-sex zemirot, as well mixed sex Jewish youth groups (similar to Benei Akiva and NCSY). He interpreted the Rambam that the prohibited form of "gazing" and listening is only that which entails sexual pleasure. Rabbi Weinberg also relied on the Sedei Hemed (section Kuf, kelal 42), who ruled that a man's listening to a woman sing funeral dirges does not violate kol ishah, as no sexual pleasure is entailed in such songs. The Sedei Hemed was relying on the Divrei Heifetz (113b), who "stated that as long as a woman is not singing sensual love songs, and as long as a man does not intend to derive pleasure from her voice, there is no prohibition, such as if she is singing praises to God for a miracle, or is singing a lullaby to a baby, or is wailing at a funeral."  Rabbi Weinberg also cited the Sefer ha-Eshkol (Hilkhot Tefillah sec. 4 or 7), that listening to a woman sing is prohibited only where there is sexual pleasure. Rabbi Weinberg reasoned that if the Sedei Hemed could permit funeral dirges due to their lacking sexual pleasure, then he could permit Shabbat zemirot on the same grounds. It is obvious that we today can likewise permit by the same logic any song which does not lead to sexual thoughts. Thus, this interpretation that kol ishah is like etzba ketana, i.e. permitted where sexual pleasure is absent, is not only apparent from the simple meaning of Rambam's words, but is also endorsed by Rabbi Yehiel Weinberg.
Rabbi Weinberg also relied on the opinion of the Ritva and Rema, "that all is for the sake of heaven" (to be discussed later in this essay). In general, if one knows that he himself is capable of a certain act without incurring sexual thoughts, then this act becomes permitted for him.
I am inferring from above as well as the rest of the article, that the main concerns are related to singing. As you can see, there are leniencies, there. I think that hearing a woman speak is less of a concern of Kol Isha.
If your concern is regarding mixed seating, I can say from my personal experience, that I have attended numerous services where there was a mechitza for davening. A woman gave the D'var Torah before Musaph on Shabbat, and she went to the front of the shul, and the mechitzah curtain was drawn so that the women could see her. It was a given, then, that the men could see her as well as the other women.