You can go with whatever you like, man. Personally, I'd go with dedicated midbass in the rear so when you do get a sub, you'll have something to fill in between what the subs and components can't. For now, just focus on the front stage and get that sounding as good as you possibly can. After that, move on to the next step. Nothing is more frustrating than taking on a whole system overhaul and having to fine-tune everything at once.