When looking at Legacy speakers, and considering bass performance and sub or no sub, bear in mind that Legacy measure pretty flat, i.e., unlike some other speakers, Legacy does not boost the mid bass. Some companies boost the mid bass, so as to give more of that "slam", but that is not necessarily accurate, and may give the impression of more/better bass than the speaker actually has. So, while the Classic HD go down to around 30Hz, you may still end up wanting a sub, but you could do that later.
OTOH, as mentioned above, the Signature SE is certainly the way to go if you can swing it. Think about it this way: if you go with the Classics, and then end up buying a subwoofer, you could have applied the cost of the sub to a set of Signature SE!