Changing logitech z5500 subs

Your just swapping the speaker? Get the speaker that the system requires. If the existing speaker is 2 ohms, you need a replacement with 2 ohms. Mismatching this number could smoke up the voice coil, or worse, the amplifier. I don't have any special recommendations for brand, but get name brands. Also, try to get dual voice coils and match up the wattage. Higher wattage speaker means it may be quieter, lower wattage may mean louder. But if you get lower, it makes it a ton easier to blow the speaker.