good monitor speaker for a large room

You may want to consider the Totem Mani-2. With enough power driving it, it will fill your room with solid bass. No need for subwoofer.

Active Event Opal with built-in near 500wpc of total power each plus room correction pots beats with price and performance models priced 5x as much.

No doubt different speaker and stand combinations present different requirements for optimizing their synergy. So don't just assume that heavily mass-loading the pillars of stands will dampen the bad stuff and give you the best sound. Peter Comeau, the U.K. loudspeaker designer associated with lively sounding designs at Heybrook and Mission, as well as the (apparently) strongly reviewed recent budget offering from Wharfedale, the Diamond 10.1 [I believe] recommends, instead of sand or lead shot, to use KITTY LITTER. No kidding. The idea here is that all that mass leads to energy storage and its delayed release, smearing the sound and compromising the PRaT factor.

So I'd suggest bagging that sand/shot so you can cleanly experiment. Something like 6-8" of sand & shot mixed, plus a fill of the kitty litter might -- just as one example -- give you an ideal combination of stability and speed. That energy storage factor could possibly be exacerbated by having to fill a larger room from stand mounted boxes.

It would seem that a lot of mass would allow energy release from the speaker. The driver is moving in and out to push a sonic wave forward and into the room.
The more solid the platform (mass), the more energy released from the driver.
I'm sure there are speakers that might benefit from a low mass dampening material such as kitty litter.
I'm not going to empty my stands to find out.

you must investigate and try if available the Mark and Daniel Maximus Monitor+. It should be a great match for your space and listening requirements. http://www.audiogon.com/cgi-bin/cls.pl?spkrmoni&1318733858&/Mark-And-Daniel-Maximus-Monitor