I’d find the best spot for the velo and use the the other two in the garage or bedroom or something like that. OR sell the other two and get something similar to the velodyne. Which model is that?
Like HD said, the better sub is always heard back and that also includes linearity. The DT and klipsch both won’t be as good as the velo in linearity or output or extension. For that matter, an updated subwoofer could also be an improvement in fidelity, but my hunch is that you want to at least keep that. So I’d use it by itself.