I can't get over the size of that room - It's as big as my house. (Yes, I'm jealous)
Which leads me to suggest that you don't overlook bigger Tannoy HPD or Goodmans Magnum K bar fridges. Perhaps older big-inch JBLs and other Americans might also be worth considering. The USA is the land of the big room, and older speakers, from when watts were much more expensive, might be less likely to stress a period-appropriate low-power amp? Maybe.
Can you 'try before you buy'? Or 'buy before you try before you sell'? The latter approach is quite popular with some. Of course others favour the 'buy and maybe try before you store' method, also known as 'hoarding'. Or is it 'collecting'?
When you say "Without the sub these speakers battle to keep up with the bass", do you mean there is too little bass (which would be my interpretation) or the bass is 'flabby' perhaps a.k.a. 'slow/boomy'? (which might have been thenoizeguy's interpretation). Sealed cabs are traditionally less efficient than aerated cabs, according to the pamphlets I have read, so that might work against your need to enlouden the room.