I would get a dual sub system in order to have a flatter response. The ULS-15 will easily outperform the Rythmik sub, in fact it would probably outperform two of them, but that is more headroom than you will likely need. If you like to crank your system, the ULS-15 will foot that bill. But if you don't need that much headroom but want a nice black gloss sub, look at some SVS SB-2000s in gloss black. If you want more punch, look at some SVS SB-3000s. In this price range, its also worth looking at the Paradigm Defiance X12.