i assume you had the jumper correct and you could boot the sdcard.
Even with the SD-card in the right orientation and the jumper in the correct position the controller boards without the U6 chip do not boot from SD-card.
Good luck if you decide to try it, post back your results!
In the end the solution was quite simple and it even is much easier than installing Braiins from SD-card.
First I used
ASICseer to remove the signature check, and immediately after this I used the
Braiins OS+ Web Package to upgrade to Braiins from the web interface.
No need to flash older Bitmain firmware first, and no need to take the miner apart and move a jumper back and forth.