He said they're 4 ohm DVC, so that would mean each woofer could be wired to 2 ohms or 8 ohms.
That would mean you can get away with any 500ish watt RMS amp @ 1 ohm, which are a dime a dozen and cheap.
I'm very partial to Sundown Audio. I used to work for them as a sales rep and the entire company is top notch.
Yeah I know. Each sub is wired for a 2 ohm load. So with the combination he has, he will have to get a 2 channel amp to keep the total load per channel at 2 ohms. With a mono amp, he will either end up with 4 ohms or 16 ohms on that one channel.
Those subs are rated for around 200w RMS each. So to run both of them, you need an amp that puts out 400 watts RMS at the specified resistance. So if he ends up with a monoblock amp rated for 500w RMS at 1 ohm, it will not have nearly the power all the way up at 4 ohms.
To use a monoblock amp with his setup, he will end up with 4 ohms. To get a monoblock amp that is rated at 1 ohm to still output 400w at 4 ohms, he will need a pretty big amp, probably close to or over 1,000watts at 1 ohm. That's why I said his best option with what he has, is to get a 2 channel amp rated at 200 watts per channel at 2 ohms. Will be much cheaper, easier to find, and more efficient. There are a million ways to do it with wiring combinations, and different amps, but that is what I would do in his position. A 2 channel rated at 200 watts per channel at 2 ohms, and hook each sub up to its own channel.