There are a LOT of variables to the Polk document. Saying not to use the sub out of a receiver is a gross oversimplification of a POSSIBLE problem. Right off the bat I noticed that both of my Denons (1801 and 1803) do send bass to the sub in Stero mode. Second not all subs force you to use the built in crossover. My Athena and Energy subs have a cross-over bypass mode. Third the graph at Polk's site shows a ragged frequency response because of interaction between the two low-pass filters and the satelites. Cross-over slopes are always a compromise there actually are conditions where higher rate slopes are desired. Without mesurements there is no way to speculate as to what the resulting sound will be. Fourth, using high-level (speaker) inputs to drive an entire speakers system negates the benifits of bi-amping (everyone with an active sub is essentially bi-amping) - when your receiver clips for any reason, in the treble of the bass, distortion (IM or HD) will be realized elsewhere in the audio band.
The document does have merit in that it points out a possible shortcomming to using the sub-out jack.
Check how your receiver does bass management in stereo and measure the results to be sure you are not having this problem.
just hooked up my Polk RM 6000 speakers using their method. The reciever is Yamaha RX-V430. Both are entry level products but I am very pleased with the sound and the price. I watched Armegeddon and it sounded fantastic. Polks method I questioned but it works very well. Bang for the buck is the answer. An audiophile I'm not but to the average ear I think its hard to beat this. The rather small 8" sub kicks butt when its hooked up "Polk Style" and I'm in for around 6 hundred$ total investment-- rock on BV
I did notice that setting my front L/R bookshelves to large instead of Small made a huge difference. Using polk suggestion you will not get the .1 sub bass track as far as I can tell unless I'm missing something. Another sub company suggests simlimar but stating to also use the sub out along with the speaker high level outs. But then I also read most speaker companies say not to wire both ways.