Large room with low budget for speakers

Sounds like a troll post.  $30K budget is low?  Definitely a first-world problem.  No dealer willing to work with you on that budget, or do you just like trolling forums to stir the pot a bit?  If you've really got an array of REL subs, why are you worried about low bass response on your mains?  Get serious.

Mornin.  What I’ve found effective for my 30x14 x15 room has been a system using double advents. On all our 5 channels  with your subs on the front 3 channels.. just mAke sure the 10 speakers have the “ fried egg tweeter”.  Original woofer if possible , ..   gonna need 3 channels of  amps for fronts .. powered subs also .  All this should be possible within your budget. .. let me suggest odyssey 3 channel outlaw receiver for surrounds .. preamp outs for front.  Speaker level to drive 3 subs… provides the 5 full range you need for sacd.  Read Harry  Pearson  double advent review in one of the first “absolute sound” issues

GoldenEar Triton Reference. Built in powered woofers, 1800 watts rms. Stereophile class A rated. $11,000. I have 26'x32' room. They sound great.

5000 square feet is not a small room. My whole house is 1100 square feet!!! What do you live in, a palace?

That's not so big of a room that you can't find speakers.

What about some of the big Tannoys or Klipsch La Scala?

A 20 x 30 room with 8' ceilings is 4800 cu. ft.. Most average to large speakers should be able to fill that room with sound if the acoustics are reasonable.