Thank you for your post. We would expect the same response for either 0x56 or 0x57. You only have to request one of the register's addresses to get access to its entire contents (16-bits). I wonder if the communication is only catching the first or last 8-bits of the response. What do you receive when you read ZACCL_OUT, when the device is sitting flat on the table, where we would expect the response to be close to ~1g, or ~0x04B0? You might also want to observe the SPI signals on a scope to see what the device is actually receiving. Let us know what you find out and we will be glad to help.
Thanks again!