AFAIK, Forum is their beginner / student line of drums, but that doesn't neccessarily make then "crappy".
I get the feeling you either haven't been playing for very long, or haven't changed out heads all that much.
Give it some time and work at it, you'll come around....you know the old saying, "practice makes perfect".
As for your tom head question, you can use any combination of any head on a tom (or a Bass drum, for that matter), as long as its the proper size for that tom.
Its all about the sound you're looking for.
I suspect, since you have Ebony Ambassadors on the batter side (top) of those toms, and the stock heads on the resonant side (bottom), the resonant side heads are thinner, in this case.
Look and see if the word "resonant" doesn't appear on those stock heads.
Those tend to be lighter weight heads (what Remo would call a "Diplomat"). While you could play on them, they're meant to accentuate the resonance of the tom.
A thinner (or "lighter weight") head will tend to do that. The effect is similar to the sound you hear from a tympani, in that its "bigger" and more resonant, compared to using a set of Ambassador weight ("medium weight") heads in their place.