IA's site says
1800 watts x 1 at 1 ohm
900 watts x 1 at 2 ohms
450 watts x 1 at 4 ohms
Strapable Pair 3600 watts x 1 at 2 ohms
Two DVC 1508's will be about 1, but rise a good bit. I would say on Music that you will only see in the mid 900's and they will take that easy.
I was metering two 1508's on a DD M2 yesterday, Input Current was peaking at 120amps at 12volts or 1440 watts into the amp, assume 80% effencent and they were seeing about 1100 on the two. Took it easy.
We have one setup with a Memphis M class 1500 at 2ohm on two of the SVC's Guy beats it hard they are now about 4 months old and doing great.
I would suggest you do 3 1508's or 10's on the IA40.1 get the DVC's and put the box at the mid or lower end of the DD Spec.