I could see two options, a 6110 stream on one end turned down slightly. Or since you mentioned visibility 2 4002 pumps positioned back center blowing into the front corners. These are top mounted and the only draw back is the need for bearings and maintenance every couple years. Also the controller for the Classic style pumps are more expensive.
The 6110 $325 is your most cost effective, slightly intrusive at a 4.5" cube, tons of flow, may disturb the sand bed. Ideally you would put your flow from return through a 1" sea swirl on the other end.
The 4002 set will cost twice as much about $700, only part in the tank is the intake, probably will disturb the sand slightly, more intricate control is possible with the 7082/2.
These would be my suggestions.