I love the Focus XD also, but pairing with an external integrated amp is not straightforward. The subs internal to the XDs must be powered by the internal 750 watt amp, and that amp has no input trim. It's unlikely that the gain on the integrated is exactly the same as the XD internal amp.
The Legacy And Wavelet external crossover is a popular solution, but at $8k, it's a budget buster in this case.
The Focus SE is a good option when there's a desire to use an external amplifier with minimum fuss. Where there's no external amplifier, the XDs can be entirely powered via the internal amp.