The Warm and QTUBE voicings of the V803 are both based on the tone of a classic, vintage tube bass amp. Upon first play, you may suspect that these two voicings are actually identical. But this isn't fully the case. Here's the difference between the two:
Warm - Tube-like output character with bottomless limiter.
QTUBE - Tube-like output character with ordinary clipping at high gains.
Essentially, the QTUBE voice will be dynamically different than Warm. Without the bottomless limiter in play, you will be able to achieve a more breakup with your Gain up adequately.