I'm familiar with your amp and your speakers, and with the issues of sub setup.
I currently own a Pass XA30.5, and I previously owned a pair of Focal 1007be's. I crossed over the 1007be's at 80Hz into a JL Fathom 113. The system was EQ'd with Room EQ Wizard and Meridian Room Correction. The results were excellent.
IME, the two simplest and most effective methods for subwoofer setup that require no equipment other than a SPL meter are...
METHOD 1: Optimizing frequency response. Place the sub at the listening position, then walk around the room and listen for the location where the bass is the most *consistent* across low frequencies. You can do this by ear with music, or you can use a SPL meter and low frequency test tones. Once you find the location in the room that has the smoothest frequency response, place the sub in that location. Now the bass response at the listening position should be in pretty good shape.
METHOD 2: Optimizing transient response. IMO, good transient response requires time aligning the sub with the mains. A procedure that can help with time alignment...
1. Flip the polarity of either the sub or the mains (but not both).
2. Play a test tone at the crossover frequency.
3. Use an SPL meter to measure the output level.
4. Adjust the sub position (or digital delay, if you have that capability) until you MINIMIZE the SPL at the listening position.
5. When the sub is in place, flip the polarity back so that the sub and the mains are the same polarity.
In steps 1-4, you are essentially maximizing the *destructive* interference between the sub and the mains. In step 5, you are restoring the sub to the correct polarity, which now maximizes the *constructive* interfere between the sub and the mains. That will help with both frequency response and transient response.
IME, the first method is the best place to start. When the sub is roughly in position, use the second method to fine tune.
Fair warning, good sub setup requires you to be systematic and patient. But the results are well worth it.