Instead of a completely subjective analysis, I included a simple spectral analysis of each speaker system. I've never done this kind of analysis before this review, and found that it requires a fairly elaborate setup and calibration to be done perfectly. I didn't have an SPL meter to calibrate the absolute sound levels, so keep in mind that these graphs are not perfect, but they should accurately show the differences among the three 5.1 surround systems.
We can see from this that the Logitech is a bit bass-heavy, as there is a high trend from about 30 to 130 Hz. Other than that, it's fairly flat on average, with a gradual but very slight downward trend as the frequency gets higher. Keep in mind that the smaller bumps and troughs can be caused by things other than the speakers, like the characteristics of the room.
Creative G550W's Sound Like
Creative's 5.1 system produces a sound that is a bit flatter and more consistent throughout the spectrum. The bottom end is still stronger than the rest of the spectrum, but it's not nearly as pronounced as the Logitech Z-5450s.
Altec Lansing FX5051's
The FX5051s show strong bass, and unlike the competitors, a peak at the high end of the spectrum as well. This can probably be attributed to the fact that the 5051 is the only system in this review that has a separate tweeter in each satellite, in addition to a larger driver. Other than these two spikes, the Altec Lansing's output is fairly flat.