Use a single amp. How you wire the subs depends on the ohm load of the coils and which amp you're wanting to run. With the IXL's, you have dual 2ohm coils on each sub. So you can wire them to either 4ohms or 1ohm for each sub, which when wired all together, can give you either a 1.33ohm, .33ohm, 12ohm, or 3ohm load, depending on how you wire them. The obvious way to do it is either 1.33ohms or 3ohms since there are a lot of affordable 3kw amps out there to run at 1.33ohms, or you can bridge two smaller amps to the 3ohm load.
Hopefully you have an upgraded electrical system to handle that kind of power.