Ok. I'll try to help.
First, look at your room. If you dimensions are correct, you will want to budget (at some point) for acoustic treatments to deal with the many issues you will have with a completely square room. You can research this later if interested.
Second, how far are you going to sit from your speakers? How loud do you want to listen? Only movies, or music too?
Third, look at speaker sensitivity, nominal impedence. Both are important in choosing a receiver/amplifier. Your main speakers are 90db/watt at one meter and are a nominal 4 ohm impedence (but the manufacturer states you can use an 8 ohm receiver). So, they can get fairly loud with little power, but since they are small (they are small, by the way) they will compress before getting SUPER loud (physics of small cabinet/drivers).
So, if these are your speakers, then you will do fine with a receiver that is capable of driving a 4ohm speaker and anything over 100 watts would probably be wasted anyway. I would also ALWAYS by one superior sub over two inferior ones. So, if you can spend 600 dollars on two 300 dollar subs or one 600 dollar one...I'd choose the better one. Your room will have issues a second sub will not be able to correct.
Did I help or confuse you?