With DX200 and Amp 4 specifically: I can't recommend it more highly.
Edit: to make the answer a bit less vague, check out the impressions of the Phantom on the Empire Ears thread and/or Ranking the Stars. I've posted impressions there as have others. What the DX200 with Amp 4 does is ensure you bring out the best of the Phantom - fantastic, extremely deep but balanced and phenomenally articulate bass, mids and vocals that are so vivid, holographic and lively that you can't help but be fully immersed in the soul of the music, and clear, extended, natural treble to tie it all together. All with the most natural timbre you can ask for and a tonal balance that shifts from song to song depending on how the music is meant to be heard - the gear disappears and nothing is left but pure, glorious music. Unless you like Justin Bieber. Then shame on you!