that large space, I would go for larger speakers, reminder the AR-2ax have 10" woofers.
more efficient an advantage,
depending on what he buys, be ready to try adding a sub or stereo pair of subs located in-line below the speakers, as it is both primary and overtones of bass notes that give directionality and establishes and maintains imaging.
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blocked rear ports:
IF you find some nearby (avoid pay for shipping) great speakers with rear ports, as mentioned, just stuff them closed. not little speakers with ports, they need them, and not big enough for that space anyway.
I have two sets of blocked rear ports due to their current locations. main system, 15" woofers, rear port was open in prior location with no rear wall behind, closed them when I moved here with a rear wall and nearby corners.
video system: rear surround speakers, rear ports stuffed, they lay on their backs, fire up the slot between the back of the sofa and the wall 6" behind.
