If you have a bunch of words or phrases assigned to keys in Gigastudio, the only way to play them at full volume from beginning to end is to send a midi note with at least the same duration as the phrase.
There are a few options for this:
1. Actually play a key for the necessary time.
2. Actually play a key, but then hold down a sustain pedal for the necessary time.
3. Insert midi notes of the necessary lengths into a midi sequencer track, then play the sequence back.
Alternatively, if you just want to tap a key briefly and hear the whole phrase, (and the phrase is not too long), you can edit the envelope release time on EG2 (the volume envelope) belonging to the region which contains the sample, so that it has a much longer release than you need to hear the phrase. Just remember that from the moment you let go of the key the volume is dropping off. The longer you set the release time, the less obvious this drop will be for shorter phrases.