hifiron,
I had a similar problem in one house I owned. We added 2 ft. of space to the depth of the room when building and the floor became a semi-trampoline. The room was now 20' wide and 16" deep. The joists ran from front to back so they were 16' long X 7 1/4" in height. The Maplenoll Ariadne TT at 70 lbs. had trouble tracking most records if someone was moving in the room.
The solution proved to be building a beam by connecting three 2" X 12" boards together. If they are not long enough to span the distance under the joists, put the spliced beams at different locations so the strength is maintained. Glue and nail the boards together at several locations both top and bottom. Use 6" X 6" posts to support the beam. Since you are over a crawl space and I was over a cement floor of the basement, you will need to make solid footers to support the posts and thus, the beams. The footers are going to need to go below the frost line if you live more north in the U.S. That means you would need at least 3 footers 12" in diameter and 42" deep. Use heavy duty 6 X 6 hangers anchored in the footers with a 1/2" J-bolt. Where the beam touches the joists, anchor this location with hurricane straps from the joist to the beam every few joists so there is no chance for it to slip. If you run this beam down the middle of the support joists, the bouncy floor problem should be a moot point.
Once I did this, my Maplenoll tracked beautifully with even a 250 lb. buffalo like myself walking or mildly jumping. Yes, it's a lot of work. Yes, you will have to buy some materials--about $125.00 worth I would guess. But the other solutions might be better than before or they might not--this one will work! You'll be able to use the TT you like the best, too.
Try a wall mount or a stand/rack. See what you like better. By the way, I build strong decks for people I know sometimes and the name I use is Gibraltar. You can jump on my railings and still be safe.
And Geoffkait, there are a few racks where the sound is vastly improved over just about any other method of supporting your equipment--Sistrum racks, for instance. Tremendous improvement in sound with no drawbacks. Drains those vibrations quickly to the floor, don't damp them.
The sound becomes much more live and real sounding. It even allowed me to take all 4 corner bass traps out of my room--you couldn't tell the difference in or out anymore.
