the other way to achieve tremolo sounds is by not using VCA level as your destination, but simply using the amp-env amount instead (no need to use negative values for your LFO then, but make sure your env-amount is not set too high, otherwise you don't hear a lot of tremolo, since all modulation sources add up).
On your other question: I only have a mopho-tetra, so no effects there, but normally, sweeping the effects manually or with an envelope should produce similar results. Could you describe your problem a bit more detailed?