Just a quick update this time - I decided that it wasn't ideal having my HF drivers perched on top of the speaker, so I 3D printed a solution to get them a bit lower down onto the panel.
Not mentioned in this video (sorry) but I did also have to time-align them in the DSP, as the BMRs now sit a few cm in front of the panel. Luckily, the Hypex software makes this easy, as shown in my 'Basic Tuning' video!