If your room is big enough and you want the low end extension of the floor standing A/V-3, then you can reverse (flip flop) the layout of the transmission line and allow it to exit out the front side instead of the back side.
I find this very interesting, as I'd like to put the speakers about 1ft from the wall if that will work well,
for 'WAF' reasons.
My present TLs use single 6.5 inch drivers and, mainly for 'package' reasons, have the vents in the sides of the cabinets about 12 inches down from the top (speakers are 40ins tall). It works well and allows placement about 9 ins from the wall. The sound does improve slightly at 15ins from the wall but the difference for me is OK to get the WAF approval!

With the new speakers I expect to compromise and set them 12 ins out.
Anyway, just a thought or two on Danny's suggestion.
One is to try venting the TLs through the side panels rather than the rear, keeping the area the same. Might be worth a try?
The other is this; when reversing the layout to vent through the front, the braces will have to be rearranged a bit, or the highest partial brace (brace C) will interfere with the lower driver. Any suggestion how to do this please?
I've been *very* busy with a major sailing boat rebuild project all this year which is why I have not yet ordered my kit. But I am fully confident in the AV/3.