On the basis of this thread and some other sources online, I figured I'd try out a SubDude platform for the REL sub in my main system. Received it last week and placed the REL on top... immediate improvement in bass response in my room! While I appreciated the reduction in vibration that I could feel at my desk, through the hardwood floor, or even in my listening chair, I most appreciated that the "bloat" I usually heard during bass-heavy tracks had largely diminished such that the sub's output was more in tune with that of my main speakers. Success for under $100!
...and then I got to thinking, there's still a fair amount of noticeable vibration coming through from the speakers. Ultimately, I plan to get a couple sets of Ultra SS's under the O3's to properly address that situation, but while I'm waiting to make that purchase, perhaps I could do an afforable experiment with a pair of Gramma platforms..?
Yesterday, my new Grammas arrived and I managed to orient the O3's on top of them... the towers have to be turned slightly askew in order for all four spikes to fit on the platform, but it worked!
Playing music yesterday and today, I've noticed that the speakers-on-Gramma did not have quite as good an improvement as did the sub-on-SubDude, but I have observed a couple nice things: the general amount of vibration in the room has been reduced even further, and louder volumes that were previously overbearing and obnoxious are now more pleasant and listenable. I don't think I'll keep the Olympicas on the Grammas for very long, but I feel like I got a good taste for how effective speaker isolation can be.