Whoever told you 2 subs is essential is an idiot, do not go back to that shop. There is absolutely no justification for needing multiple subs. Its all about the displacement potential, which can be accomplished with 1 sub, 2 subs, or 27 subs, it does not matter. That's basic stuff there, and any installer who says otherwise cannot be trusted to perform even a basic install imo.
There's no reason to say xxx's were built to run ported, they work exceptionally well sealed. Remember, they have gobs of displacement (xmax) and an extremely flat BL curve, makes for a very loud and clean sounding sealed driver. Brahma's also work very well sealed.