I tried this during the first year of ownership but the subs I had at the time were not a good match for my 13A. So I used the speaker level connections and got very good results.Personally I'd definitely crossover the mains but play around with your crossover points and see what works best in your room. Bass is a bit different for everyone.
But this week I began again to try setting the 13A as Small and using a crossover in the processor. In doing so, I've moved the subs to more optimum placement for normal subwoofery and am in the process of getting the group to its happy place. Frankly, it seemed easier to use the speaker level connections and align each 2-stack of subs to its 13A host, and then add the subwoofers at the rear of the room to help smooth things in the 60-70Hz range where a null exists. But, I'll give it a good go and see what happens.
I've been able to get a good result measurement wise where the crossover is concerned, but it sounds different, and I'm not liking it yet. The primary concern is strictly 2 channel music.