Not sure what Rel model that is (s/510)? I did not like the standard feet on my HT1205 mkii as the sub would actually move on my LVP floors during spirited listening sessions. Ended up replacing them with some SVS isolation feet and solved that issue. The hanging pots and pans in the kitchen still vibrate once in while.
You are correct. It is an s/510. I was looking at a T9 but decided to go up their line a little bit as the room is relatively large and open and this system has been doing more mixed music and HT duty in the last few years. Despite weighing 75lbs, the s/510 can still shake itself around on the floor too if things got intense. I blame the downfiring woofer doing just enough to offset the weight enough to reduce the grip. I would have gone with the SVS feet as well but the s/510 has more a rail style support and surely wouldn't work with those. This works well becuase it still provides a solid base for the downfiring passive driver without changing the expected clearance.
After I posted, I did a quick test with a couple sequences from movies that normally shake the poop out of the room. It seems this platform is having more of a positive effect than I thought it did at first. Currently feeling a fair bit more positive about it. I should have given it the Edge of Tomorrow test but forgot as I ran out of time. I'm thinking of starting a Nolan Batman cycle tonight, so that should be a good broad test evening.
With the new amp, I was able to get ARC to give me an F6 (or F0 depending on how you want to look at requested room gain vs reference level) of 15 Hz. That's driving things pretty hard below their rated bottom end though, so I've backed off a bit and set a roll off targetting that point at 20Hz now, but it's still only 3db down from the refernce level at 16Hz, so there's plenty of low level stuff going on to rattle that border wall around it.
