If you want to get rid of dead spots, get a multiple sub system, so get maybe two beefy subs and place them apart from each other. Three subs would be even better. Look at Outlaw Audio, Hsu Research, SVS, Monoprice Monolith, if you can handle big subs. If not, look at MartinLogan or Paradigm (the Paradigm Defiance X subs are brutal for their size).