I have used Altec Lansing MX5021 and CS-21

I live in Delhi and I am using Altec Lansing speakers for the last 7 years. My first model was ACS-21 in early 2002. Then in 2004, I purchased CS-21 at 5800 rupees INR with 10M warranty. Then in year 2006, I took MX5021 at 7000 INR

No doubt that MX5021 are THX certified and their frequency response is 30 KHz to 22 KHz, but the system SNR is near 80 db at frequency of 1Khz and their peak power is 90 Watts RMS and maximum sound output is 103 db (SPL). The peak power of CS-21 is 110 Watt RMS and SNR is 86db at 1Khz and max sound is 108 db (SPL).

The frequency response of CS-21 sub-woofer is 27 Hz to 113 Hz and of MX5021 is 40 Hz to 150 Hz. In CS-21, the RMS wattage is 30W/satellite. You can compare it with other brands like Logitech and Creative as well.

The bass depth is more in CS-21

The main criterion is the input impedence, SNR, linearity when amplifier is driven too hard, THD, etc.

THD value of both is too poor.

In short the sub-bass level of CS-21 is much more than MX-5021. The amplifier of CS-21 is much more. In CS-21, the amplifier power is much more than the requirement of satellite and sub-woofer and that is why at maximum loudness, the audio is not cracked. The amplification of CS-21 is linear. However MX-5021 amp is like Aiwa. After 87% of amplification, the amplitude of LF component is not increased in order to avoid crackness of audio.

MX-5021 are expensive than CS-21 only because they are newer model (with IR remote) and they are THX certified.

The audio clarity, especially the mid range of CS-21 is more because when its amplifier is driven too hard, it remains linear and audio is not cracked. CS-21 means Concert & Stage.

If you use MX-5021 even in a room, then you would not hear sub-bass frequencies in another attached room. I m currently using MX-5021 with Creative Xi-Fi Extreme Music and CS-21 with SB Live 5.1 Digital (sb0220). After 5 years, my CS-21's audio is not even 5% degraded.

Instead, I have experience of Logitech Z-5400, and I surely use AGC/compressors and other DSP enhancements.

Right now for Computers, I prefer Altec Lansing FX 5051 speakers powered by creative sound blaster X-Fi Pro Elite sound card.

For home theaters, I prefer BOSE Lifestyle 38 Series III DVD Home Entertainment System with 10.2 surround sound system.

I also tried a few 2.1 speakers but finally settled on Philips MMS 430. They simply rock. The bass is really good and tight and it is well balanced by the treble. Got for it at 2700 INR. I had tried Altec Lansing BXR 1121. They were available for just 1350 INR. Although they look great, they sounded a bit flat. Next, I tried Creative SBS and M2600, priced at 1200 and 1800 respectively. Surprisingly, the SBS sounded better than M2600. But they both did not sound good although at the computer shops, they were selling like hot cakes.