Big, big room -- which 10-20k speakers?

Well, I'm a bit late responding, but, since no one has mentioned them yet, here goes.

With your stated tastes, you actually won't need super-efficient horns, etc., to listen to lifelike levels of music, IMHO. My only caveat is that I have been to some rock concerts where the sound was so loud I had ringing in my ears after the concert...I'm presuming you aren't seeking that level of sound pressure!

First, as noted above by Bvdiman, your Luxman is 'only' rated at 120 WPC for 8 ohms. However, the 509u's 240 WPC rating for 4 ohms is normally a good indicator of an amplifier design that does have the ability to deliver enough current to properly drive most speakers.

I believe you really owe yourself a trip to audition the Magnepan 20.7 speakers. Magnepans (when properly placed) will fill a large room with the most lifelike music I've ever encountered. Dating back to their beginnings, when the Magnepan Tympani was declared their new reference speaker when reviewed in The Absolute Sound, Magnepan has repeatedly raised the bar vis-a-vis lifelike musical reproduction.

When paired with a superior subwoofer that can accurately produce the bottom half of the bottom octave of music (I presently use an M&K, and would suggest you consider the M&K MX5000 with the upper filter set to coincide with the 3db rolloff point of your main speakers) I've found that friends who have invested a LOT more than I have marvel at the natural musicality of my Magnepans.

Yes, I know they aren't the most efficient speaker ever manufactured. Yes, they do require placement away from a back wall to produce the best sound (one reason they sound so good in a larger room?). No, they don't have some magical unicorn horn dust sprinkled on the unobtanium drivers or the snob appeal of some unique designs. What they do so well is allow you to close your eyes and 'be there' with a recreation of the recorded performance that can be stunning.

I wish you good fortune with your quest!

I don't see the problem with a big room. In fact, the big room minimizes of a lot of potential problems that are the bane of smaller rooms such as early reflections, standing waves, inability to get the speakers away from room boundaries, etc.

If the intent is to fill the entire room with live sound levels, then not only are the speakers named not going to do the job, as has been pointed out, the amp isn't going to do the job either. To really pump out the SPLs without spending a small fortune on one or two super-amps, horns are about the only solution. That's just physics.

I've lived with a set of Edgarhorns for almost ten years, and while there is a lot to like about their efficiency, their uncanny dynamic jump, and their ability to play really loudly with just fractions of a watt, they are not the speaker for everyone. And, they can be hard to find used (and I don't know if they are available new anymore, though I just retired mine and would consider sending them to a good home. . .).

If however, you can live with sitting 10-15 feet from the speakers in the sweet spot for serious listening, and will be satisfied with less than live levels elsewhere in the room while other activities are going on, then just about any reasonably efficient speakers will do the job.

I'm currently using KEF 207/2s and with their 91db/w/m efficiency they do a very good job playing at levels as loud as I would ever listen within 10-15 feet. Even new they come in right around $20K.

If sufficient bass becomes a problem, there are any number of good self-powered subwoofers on the market. A stereo pair, positioned to make some use of boundary reinforcement would likely solve that problem, if it actually is a problem.

As far as room treatments -- go slow and do your homework first. Check out some of the websites (RealTraps, GIK Acoustics, ATS Acoustics), get some tools such as StudioSixDigital's AudioTools for iPhone or Android, and take some measurments. You might just find that your problems with the room are really minor.

Good luck!

My room is 28x28x12 cathedral.
The Evolution Acoustics MM2 solved all the problems
I tried many speakers and almost gave up on bad sound until the MM2. They fill the room magically.
The biggest problem with other speaks was always the bass or the foundation of the music. I think the powered woofers are the answer.
Other speakers I have tried but never cut it:
Dunlavy IV, IVA,V
Von Schweikert VR7SE

I Also could never integrate subwoofers correctly but had plenty of bass.

Evolution Acoustics MM2 are also adjustable

Thinking along the lines of Snook2, I would seriously consider getting a full range speakers and adding 2 powered subs (for example JL113). This will be more cost effective than a speaker with large woofers, gives you far more options, more placement flexibility and you can typically EQ the subs (eihter build in or separete sub EQ box.

You will need a very large horn loudspeaker or line array to fill such a space. Maybe consider used or custom built in your price range.