According to Supercard Fourms, Supercard DStwo Players confirmed that Supercard DStwo work on 3DS V3.0.0-6 E /U /J well ! please see the below quote :
"It seems that this time firmware have nothing matter with flashcart,it doesnt block any cards. I have tested my DStwo after i updated my 3ds ,it works well. "
--Bonnie"my dstwo stopped working after 3.0.0-6E update , and it was working great with 3.0.0-5E.. i've got black 3ds zelda 25 aniversary edition" --dreamboy23
"mine works again, i've just reflashed again with the same fireware that i had -.- at least it works. followed this tutorial again.. "
--dreamboy23