Engine mount / loud vibration through frame

It makes a really loud vibration sound that is worst when the car is in drive. The vibration gets slightly more intermittent when the car is hot. I have changed out both the upper and lower torque engine mounts on the passenger side (they were indeed broken), but the vibration did not change. I then replaced the transmission mount, which turned out to be fine, but with everything apart, I changed it anyway. Vibration still there. I had someone look at the main mount at the front of the engine, but they said besides it being "a little soft" it seemed OK. I read somewhere in these questions that the front main engine mount may actually be causing the vibration after all. My question is, could my problem be caused by this mount? Is it fluid- or air-filled, and when the car is hot the mount starts to perform better? I don't want to have another situation like the transmission mount, where I pay for all the labor and then find out the mount is fine. Advice?