For the LimeSDR-USB I’ve only seen support for the transfer of 12-bit, 14-bit and 16-bit samples across the USB bus for RX and TX ( https://github.com/myriadrf/LimeSDR-USB_GW/blob/master/src/rx_packets/compress_v2.vhd and https://github.com/myriadrf/LimeSDR-USB_GW/blob/master/src/data_manipulation/decompress.vhd ).
And the same is true for the LimeSDR-mini ( https://github.com/myriadrf/LimeSDR-Mini_GW/blob/master/LimeSDR-Mini_lms7_trx/src/rx_path_top/bit_pack/synth/bit_pack.vhd and https://github.com/myriadrf/LimeSDR-Mini_GW/blob/master/LimeSDR-Mini_lms7_trx/src/tx_path_top/bit_unpack/synth/unpack_64_to_48.vhd ; https://github.com/myriadrf/LimeSDR-Mini_GW/blob/master/LimeSDR-Mini_lms7_trx/src/tx_path_top/bit_unpack/synth/unpack_64_to_56.vhd ; https://github.com/myriadrf/LimeSDR-Mini_GW/blob/master/LimeSDR-Mini_lms7_trx/src/tx_path_top/bit_unpack/synth/unpack_64_to_64.vhd )
So in my mind the answer would be that there is no current support for 8-bit over the wire samples. For that you would need to throw away 4 bits and then the question becomes which do you choose the top nibble or the bottom nibble to discard.