Stupid question time.
In your Rei folder do you have the firmware.bin and firmware90.bin? Both need to be there, and 90 specifically if you want to boot to a 9.0n nativefirm emunand/sysNAND.
If you have both, hold L when turning on and it will boot to sysNAND with sig patches and 9.0 nativefirm. From there you can launch HBL or CIA installer of your choice or run D9.
If you're loading D9 from a boot manager, decryption doesn't work.