HDMI video and HDMI audio are 2 different things- I don’t know how well the $40 converter you’re referring to will handle audio reproduction either. The DOB unit that @yyzsantabarbara mentions has been highly recommended- but I’ve never tried one with my Oppo unit.
I believe the Bryston BDA 3.14 dac will do what you’re asking for. I’ve read that it has the ability to process audio via HDMI and a pass the audio out. You’d need to confirm that for SACD as I read about this some time ago.