According to the chart that Jaws posted on page 11, the 1.5" drains are rated for 1400gph each, with no restrictions. You will have restrictions, such as valves, elbows, etc. Even without them, you will be maxing out the drain rate of 1.5" drains with two at 2800gph. Then, with the 2", you can only flow 2200gph through a single 2" line, which leaves 600gph for the "trickle", which won't be quiet. All of this combined, I think your best option is two 2" siphon drains and one 2-2.5" emergency drain. This should be an extremely reliable setup for a 2800gph flow rate. My tank is a bit smaller than yours and I run a total of three 1.5" drains, so I think a total of three 2" drains will work out well for you.
The trickle is quiet because of the upturned elbow atleast thats how i under stood it.
Id feel more comfortable if someone who has hands on with bean animal helped him i dont want to chime in on something dont have experience building myself.
not many active members talk about bean animal. Maybe herbie is just easier plumbing wise..mhhh