Yeah, today's streaming devices are not designed with the audiophile in mind. Amazon Fire removed their optical output years ago and Roku doesn't have this either. Most of these are targeting people who just mount a flat panel TV and call it a day.
You could try to get an "HDMI Audio Extractor" like the Panlong or J-Tech devices (under $40). I don't know how well these work. But your best bet is likely just to buy a newer receiver.