Originally Posted by HafX
I would definitely put money on the fact that the Polk subwoofer you recommended with the speakers and receiver shown will not come close to a boxed Z-5500. My reasoning is that I have owned that subwoofer in the past and have used a receiver etc, and unless he plans to drop well into the $800-$1000 range for a multimedia home system then nothing can compare in price to value.
Maybe if you're strictly going for a 5.1 setup, but Logitech boxed sets (even their flagship models) aren't hard to beat. If your Polk sub sounded that bad then the crossover was set too high.
Here's the biggest problem with speaker sets like the Z5500: The speakers are too small. Because of this, they can't go very low, usually not much lower than 200hz. So what do you do? You have the subwoofer take over the job. When you do this, your bass gets muddy and your lower-mids get boomy. I believe the Z5500 has it's crossover set to 120hz. Ideally, you want it to be set to 80hz or lower, that way your bass is cleaner and you can't tell where the sub is coming from.
The speakers also don't have a tweeter, so they expect the satellite to cover it with just the speaker. This makes it harder for the speaker to cover the really high frequencies.
Don't get me wrong, for a 5.1 setup they're a good deal. But if you don't want/need surround, then I feel you're better off looking elsewhere.
Edit: I'm an idiot, the receiver I linked above doesn't even have a subwoofer out.