I wonder were the "when they're pinging they're not listening" argument comes from? A single DD is capable of "pinging" and "listening" at the same time. When there are more DDs around, usually one "pings" and everybody listens.
Your sub is capable of "pinging" and "listening" at the same time, so why not a DD?
And yes shallows and DDs don't make a good combination for subs.
.