I didn't have a Series, just a Rogue, but had used a SVT-III Pro for a long time with it. Consider that I'm not a rocker and my SVT isn't a all tube amp (some friends says that they are a totally different beast), but had the same impression Jazzy wrote about. Also consider that, tone wise, I'm more fond to fusion bass tones than Geezer Butler ways.
I associate Alembic to a hifi sounding bass (clarity, open glassy tone and fast transients), and feel the grit Ampegs have compromise that somehow. Also seems that tubes sort of compress the transients and although it makes my tone deeper, I miss the top end clarity... Can't describe what bothers me (and this tone could be appropriate for rock) but it sounds less distinctive to me, less Alembicy somehow.