Russelas,
Traditionally, most people with marine FO tanks stick to W/D or trickle filters, since their tanks are usually overloaded with fish. Especially in this case, if the show tank is meant to be impressive. However, using a trickle filter would automatically mean that your NO3 (nitrate) levels are going to be sky-high unless you do very regular water changes of reasonably large amounts.
DSBs as hippo mentioned would enable the generated nitrates from the incomplete nitrogen cycle as caused by a trickle filter to be broken down back into nitrogen gas, thus keeping it low or even at zero levels.
I've set up a 180G predator tank before with a 4" DSB and 220 lbs of LR and a huge skimmer. The tank had 3 panther grouper that started off as 2" juveniles, and ended up being 11" monsters ! Then there were 3 other groupers and a couple of trevally and snapper in there as well.
When the fish were still small, keeping the NO3 levels low were no problem, but as their appetites increased so did the NO3 levels, until the best I could achieve was 80 ppm, WITHOUT water changes.
The problem with many large fish is that they can disturb the sand bed SO easily, but one way out for you would be to locate the DSB within the sump, and just use LR in the tank itself. Place as large a sump as you can underneath/beside the tank, properly configured for a DSB, and you can have up to 6" of sand in there. Then just place a few pieces of LR on top of this sand bed and you're ready to go.
Caution : Whilst LR and DSBs have lots going for them, the denitrifying bacteria do NOT multiply overnight. They need time to breed, since oxygen levels in the sand bed need to drop before they can do so. This implies that you have to monitor your NH3, NO2 and NO3 levels very closely in the initial stage and do whatever water changes are necessary to keep these levels under check.
HTH
Roger
