Wow, that got pretty technical for my limited knowledge of subwoofers and sound waves!
So, the gist of what was being said is that there is no dis-advantage to going with a 2 way speaker (or a 2.5 or 3 way, but not something with a huge MTM design) and adding a sub. In fact, it may be superior, and a whole lot more versatile (not wrestling with a 250lb speaker with 5 drivers et cetera). If done right, it will add weight to the music, especially when the music needs weight, such as in orchestral passages. Sound about right?