In reply to:
I have also read that a sealed sub is better than a ported one for 2.1 music playback. Is that true?
I would state that it is too broad a statement to be true. You have to look at the frequency response and roll-off. Also, you have to look at the efficiencies. Mind you, most subs nowadays are powered and they should take that into consideration.
My subwoofer is ported and includes an accelerometer to monitor and control distorted output, thus yielding a very clean sound ideal for stereo listening. It is not an ideal sub for large home theaters as it is underpowered in that respect. However, at 250W, 18Hz-100Hz +0dB/-3dB with clipping protection and less than 0.5% distortion it serves my purposes well for music and moderate home theater levels.
I believe that companies can offer higher-power and smaller sized subwoofers in a sealed configuration over a ported box.
It really comes down to your "needs" and preferences.