Sharpblue, I can attest to the change you are experiencing. I had my m60ti in my old place, it had 8 foot ceilings and I sat approx 12 feet away in a 700 sq foot area, thick wood floors and this was all on the second story. Things sounded really to me in there with my Yamaha reciever. I moved...it all changed and it was frustrating, super frustrating. But it led me into more learning about acoustics and my system.
My new space is very different. I've been here 2 years approx. It is a very large open space and has wood floors. 12 foot ceilings and an open 1100 sq foot area. So it sounds VERY different than the old place. This is all over a concrete basement. The overall sound was still the m60ti's I remember but with very reduced bass impact and didn't seem to go as low as if the bass was getting lost somewhere. As we added furniture and carpets and thick window coverings it all improved. I added a subwoofer and it helped alot, in fact it's better now than the old house and the space I have here allows me to move the speakers way out in to the room and I get a deep and wide as the speakers are soundstage.. Here's the part that I hope helps you, I moved it all down in to the concrete basement just to give it a go. Concrete floors and concrete walls, open 1200 sq foot basement, 8 foot ceilings, all the walls are covered in 2 inch thick open cell rigid insulation. Without the sub woofer, it sounds sooooo good down there. I added the sub and blended as best I could and it really sounds great.
The take away is it's probably the house and the construction and adding some de-coupling could go a long way to improve bass performance. As for everything else sounding like it has a veil over it, that could be the reflections of the room and your position relative to them but that's just me spitballing there. Bottom line differnet rooms and spaces sound different which I have experienced first hand. Having the speakers a bit higher with de-coupling under them shouldn't be an issue i don't think, again you'll have to play with that and see where the best height is, as you may not be ableto adjust the speaker height as the de-coupling platform would dictate that you may have to adjust your height at the listening position.
Maybe sharing some specifics about the size and shape of your room, furniture and windows and covereings etc along with more about your system will help to futher analyze it.
