Unbricking method here (use Porkupan's rescue package since the uboot link is dead):
https://wiki.mobileread.com/wiki/PRS...C_sd_rescue.29
But since it sounds like you now have a mixed firmware version, see if this post helps:
https://www.mobileread.com/forums/sh...72&postcount=5
I actually have a full guide I wrote if you need more help.