I don't see why 136dB can't be achieved. It doesn't state the conditions. Let's consider the following
Let's assume the Magico is a ported sub.
A single ported PB13 can do 110dB with an above average quality 13.5'' driver.
Considering a top quality 13.5'' driver like the JL has 3-5dB more output than the Ultra 13 (when comparing sealed vs sealed), a top quality 18'' driver should be able to produce at least 6dB more, so 116dB.
Adding a second driver will increase output by 6dB, so 122dB
Converting from 2 meter GP to 1 meter GP adds 6dB, so 128dB
Measuring it in room, you can add at least 8dB of room gain at 20Hz (probably more like 10-15dB), and we have our 136dB number if you do a 1 meter in room measurement.