Oranfoster:
I have no experience with a ported sub, so cannot comment with experience. That said, I would think it might be very difficult to place the sub so as to have it keep up with the ATCs -- such that a sealed sub is the way to to go. This Velodyne does a nice job, but it is not the last word in subs. It is small, which I needed for my office. I am a fan of JL Audio (have the F-112 at home), which is tighter and much more tuneful. Depending on your room size, I suggest you consider starting at the JL Audio F-110 and move larger if you need. Enjoy.
John