Here's an easy answer: If you want a 2-ohm load, get rid of one of the subs. But do you want a 2-ohm load or do you want better bass? That's the real question, isn't it?
Let's move on to adding your second sub. The same rules apply, so you now have a second load that can be either 8 ohms or 2 ohms, but not 4 ohms when we configure it as series or parallel. Hopefully, you've noticed something by now-you have two subs, but really you now have only single voice coils because you've wired them up to be either series or parallel. Now you can wire up the single remaining combined coils as if they were just single voice coils.
In the event that you chose to wire each speaker in 2-ohm mode by using the parallel method, you can now connect the two subs in either series or parallel. Two 2-ohm speakers in parallel would be a net equivalent load of 1 ohm, while connecting in series would give you a net equivalent load of 4 ohms. However, if you had originally chosen the series connection for the individual subs, you can now connect the pair as either a 4-ohm load in parallel or a 16-ohm load in series. You might have noticed that we have stepped right over the line into the discussion of series-parallel configurations. So with two dual voice coil subs, you have the possibility of a 1-ohm, 4-ohm, or 16-ohm total equivalent load. Which would you choose?
You haven't indicated which amplifier you're using, so I can't tell what load it's optimized to drive. You simply figured that there would be extra boost at 2 ohms. This comes more from a myth more than anything else, where a real honest fact gets applied to a slightly different situation while you expect the same result. As an offbeat example, think about observing a guy kiss his girlfriend. She likes it, so you go and kiss her expecting the same result. Was the result the same? Probably not.
I often will take an amplifier to class and hook it up on the test bench to allow the students to see what an amplifier really can do. It's an amazing revelation, since all of my students have opinions about which amplifiers they think are junk, but they're always proven wrong. Every amplifier we've tested in the class lab has delivered the promised output, but often with a few surprises. For example, one amplifier didn't produce its advertised power output at 4 ohms but it went well over the claim at 2 ohms. Others made more than rated power at 4 ohms but dropped off at 2 ohms. Which amp was better? Neither.
If you compare a diesel-fueled car with a gas-fueled car, they'll both meet rated horsepower. But if you put diesel fuel in the gas car and gasoline in the diesel car, neither will function and possible damage will result. Put a 4-ohm load on a 2-ohm amplifier and a 2-ohm load on a 4-ohm amplifier, and neither will do their best.
If your load options for two dual voice coil subs are 1, 4, or 16 ohms, it's pretty easy to determine the best choice. One ohm is so low that it will likely cause your amplifier to either blow up or activate its protection mode. After all, 1 ohm is so close to a short circuit (0 ohms) that we are on the ragged edge. At the other end of the range, 16 ohms is so high that a 100-watt (20 volt output at 4 ohms) amplifier would only deliver about 25 watts. The amp wouldn't suffer any problems, but it wouldn't have much work to do. Good thing amps can't get fat and lazy like us.
Most amplifiers are designed to operate best in a 4-ohm range. Dropping down to 2 ohms will likely not cause any problems, but you won't get any additional boost. In some cases, the amplifier will begin "current limiting" to prevent overheating and damage, so even if the amplifier ran well, it would likely be delivering less than 80 percent of its power. So 4 ohms is your best choice. All the people you have talked to so far are correct, but they missed the point-why would you not want 4 ohms as your target? That is why a pair of dual voice coil 4-ohm speakers won't mathematically resolve to 2 ohms net equivalent load resistance.