I can't address your speaker question but most subs have a high-level input that would allow you to go from the speaker terminals of your amp to the sub. For several brands, that's the manufacturer's recommended way to connect, in fact. That your amp doesn't have a sub out isn't a serious limitation and shouldn't affect your choice of speakers.
If you'll search the forum you'll find several threads on how to connect that way.
If you'll search the forum you'll find several threads on how to connect that way.