your not gunna get 6 4 ohm subs to equal a 1 ohm net load. you can get like ~1.3
You can send the REs about 250 i guess so 250 * 6 = 1500 which is a lot less than 2000. Thats already including head room. You should wire them up so you get close to a 4 ohm load and then youll be putting out less power.