As the title implies, I currently have a 5.1 system, and I plan to upgrade to 5.2.4. thanks to this forum, I'm looking at the Denon x4400h for my receiver. The speaker sitting will be in 3 phases: 2nd sub, height pair, and 2nd height pair.
Current sub is an Ultimax 15" in a sealed 4 ft3 box powered by an inuke dsp amp. Second sub will be same run off the other output of the amp. Heights will likely be a DIY coaxial or full range. I'm leaning towards coaxial because of the poor off-axis high frequency response of full range drivers over 3".
If you were making this upgrade, what order would you recommend?