Well I was able to successfully get past that particular one, although it may have been a fluke. I ended up doing a longer combo with 2 j.C's before the j.2C, because that was easier for me, and it still counts as a success.
Now I'm looking at the combos page, and I'm practicing on my PS3 in training mode. I am trying to do 5B (2) > 5C > 623B > 6C > 6D > 6C > Dash > 5C > sj.2C > 214C (3224 damage) but I have no idea what to do at the sj.2C part... it doesn't look like the opponent is high enough in the air to merit a superjump, so I'm not sure why it's necessary. At the same time, if I do a normal jump cancel, the hits turn blue, so I know the opponent could break out of that in a match...
Also in 5B (2) > 5C > Sekkajin > 5C > 6C > Dash > j.C > j.2C > j.D > 6C > 214C (3054 damage) my 5C doesn't seem to hit after the sekkajin... I'm able to combo with sekkajin just fine in 5B (2) > 5C > Sekkajin > 6C > 2D > 6C > 214C (2780 damage), so I'm not sure what the problem is.
Advice? Thanks