Here are two HD combos I made:
The first combo for no meter is 656 damage.
The second combo for 2 bars is 802 damage.
Also, here is another noteworthy HD combo to exploit:
j.C, s.C [HD activate] s.C, hcf+D [HDC] air qcb+C, hcf+D (FIRST HIT) [HDC] qcf+A, qcb+C, qcb+C, qcb+C [HDC] qcf+A, qcb+C, qcb+C > Neo Max = 811 damage