Leon,

I think the way you would detect if it were a transmission or engine mount issue is to use a floor jack carefully to take pressure off the component, engine or trans mount and then put car in drive (stationary) and see if vibration is reduced. Even engine mounts can be measured to see if they are collapsed - must be some post on this if you use the SEARCH.

How many miles are o your car?

Also I would inspect shocks and drveshaft flex-disc, doubt flex-disc - but always inspect the easy things first.