Thanks for the update and the pointer to the TXS0108. Do you think that is better than the MAX13035E or just cheaper? It seems like the MAX13035E is specifically designed for connecting to an SD card.
I'm not sure I understand what you're saying about the clock line. Are you saying that you e.g. connect SD_0_CLK to A7 and SD_0_CLK_FB to A8 on the TXS0108, and then connect B7 and B8 both to the clock line on the SD card?
BTW, on the subject of connecting an STM32, I'm currently experimenting with programming an STM32 directly from the Edison using a pair of GPIO lines connected directly to the STM32 SWD lines. I've already hacked a version of Black Magic Probe firmware to bitbang GPIO on a Beaglebone Black and have been able to connect to an STM32 via SWD. It should also be able to flash the STM32 and debug, but I haven't tested it yet. I'll post an update in another thread when I've tested it more.