Does the reciever have preout jacks? If so use them instead.
If not speaker level connection will work fine. You may have to run them off of speaker A. I do not know your receiver specifically, but some of them will only output stereo when speaker A & B are engaged.
The tape out jacks will only work with analog signals and would not give you any control over volume. Your DVD is a digital signal, that's why the sub did not work.