(SOLVED) SFE microSD Breakout woes ...

If I were you, I would swap which level shifter you are using for DI and CS.

Use:
DI <- TXI (ch2) <- TXO (ch2) <- MOSI
CD <- RXO (ch2) <- RXI (ch2) <- pin4

Goodness knows why Sparkfun gave the signals the names they did :roll_eyes:. Basically the mosfet shifter is bidirectional, but it will perform better than the resistor divider and is better suited to the data line, or even better still the clock line, for example:

DO -> TXI (CH1) on LV side -> TXO (CH1) on HV side -> MISO on Uno
GND -> GND
SCK <- TXI (ch2) on LV side <- TXO (ch2) on HV side <- SCK on Uno
VCC <- 3.3V on Uno
DI <- RXO (CH1) on LV side <- RXI (CH1) on HV side <- MOSI on Uno
CS <- RXO (ch2) on LV side <- RXI (ch2) on HV side <- pin 4 on Uno