If by "tremble" you mean "treble", then yes, with X-Fi turned on, it will have some substantial distortion. You have to remember, that each artist is not recorded the same way, with the same equipment. Take for example the metal band Korn - they have TONS of bass/low end, and plenty of high frequency (treble) mixed with some really rich polished sound, which would sound distorted even on the amazing sounding pack in ear buds that Creative graciously gave us, but, then take, say, Johnny Cash (early Cash), and listen to him with the same settings on your X-Fi 2, and you probably will not hear the distortion, but would rather actually sound well balanced at the highest volume, due to the equipment of the time lacking todays amazing audio technology.
Even todays artists, when comparing them to each other, like fingerprints, no two recordings are exactly alike. You just have to find the right balance with your EQ, whether it be custom, or preset, and the right X-Fi settings, that will sound right (non-distorted) at any volume.
On that note, i noticed that the crankage at max volume, is no longer blaring with the new firmware (1.21.05), which was a bummer.