I've never used a super d but I know that the alt 8 has huge but firm lows and agressive fat mids. Highs are warm but the pickup is not muddy at all. Notes kids leap from the fretboard
I personally have an SG with an Alternative 8 in it, and I used to have a Kramer DMZ-2000 with Super D's in it, you'll much prefer the Alternative 8 if there isn't enough bass in the Super D.