did you use autorcm since V6.1? Because that prevents the fuses getting burned. if not, youre not able to downgrade... if you do it anyway, you end up in a softbrick like that.
1 - Enable AutoRCM - AFAIK it should boot up when installed
2 - Restore NAND-Backup with V 8.1 if you have one
3 - I think there is a possibility to build your own NAND backup... but its not easy and i dont know how to do it
If i´m wrong.... correct me