Good question... the A/V's are 8" wide and X-series are 8.5"... both of which are over your size limit.
Am sure there's a way to tweak the cabinet plan to pick up 1/4" clearance if that's all you need, although likely would be some compromise depending on which route you take.
Depending on the main speakers being paired with and room characteristics, maybe the LGK driver can be used to build a center... it's cabinet will easily fit within a 7 3/4" space. I made a sound bar for a TV using essentially two LGKs that worked out well.
Interested to hear what input others have on this.
Good luck!