Nice report Jason and Mojo. That Velodyne DLS-5000R is a real departure for Velo and I suspect just a made in China sub labelled Velodyne for sale through the big box stores. Products like this just hurt the brand. I've never liked subs with big unflared slot vents because of all the noise inherent with that type of port. In addition FR is anything but linear, in fact its more humped than even the old SVS models. Worse, its THD doesn't decline to less than 10% until 30hz and above. No surprise it sounds so bad.
Judging by your and other reports, the EP350v3 appears to be a real winner especially at that price. It may not go as deep as a EP600 but a pair of 350v3 would be an excellent alternative and perhaps better than a single 600 because of all the additional benefits you get from dual subs. I have to find a pair to audition.