I took the time to trace everything on that board. So I have, in effect, a schematic now.
The key elements are:
- R2/R4 selects BS0=1/0
- R1/R3 selects BS1=1/0
- R5 must be a resistor (it's a pull-down for IREF)
- R6 and R7 are 4.7K pull-ups for SCL/SDA (or SCK/MOSI): needed for I2c; for SPI?
- R8 connects D1 (SDA or MOSI) and D2 together: needed for I2c; must be NC for SPI
BS2 is connected to ground
For SPI you want BS0-2 = 0,0,0 so that means R4 & R3 but not R2 or R1. We know this works.
For I2C you want BS0-2 = 0,1,0 so that means R4 & R1 & R8 but not R2 or R3. We both know this doesn't work!
Just in case their cable somehow connected the BS0-2 pins a little differently (the datasheet is weird on this subject), I tried R2 & R3 for I2C. But it didn't work either. So I don't know what the problem is with their board.
I also lost a couple of those tiny surface mount resistors. In both cases I set them on the table and forgot about them for a minute. In that minute they disappeared forever. But it doesn't matter since R1, R2, R3, R4 and R8 don't need to be resistors. You can use a little piece of wire or even a solder bridge.
I put my board back into SPI mode (with solder bridges) and will probably leave it that way forever... unless I hear about some new idea from you.