I've got a new pair of 533PT's and run one sub a little less than 3/4 and the other at about 1/2. The reason for the difference is that one is very close to a side wall and it'll get boomy if it's too high and the other points into a large open space that sucks up the bass so I crank it up.
Overall, I really like the speakers which are a big improvement over my 20-year-old Polks. The Polks are also very good with excellent clairity and imaging but they use 12" passive radiators to improve the base vice a powered driver. There's no comparison between the two low-frequency capabilities. The PT's had a bit of "edginess" to the high frequencies at first but that appears to have gone away with some break-in.
The only problem I've had is trying to get everything balanced properly. These speakers are the first two parts of a HT setup so I want to be able to really crank the bass but the best bass location isn't necessarily the same as the best position for the mid/high ranges. Also, I've noticed a slight weakness at the lower mid-range which corresponds to a dip in the PT's frequency response curve at 100hz. This is not normally noticiable; however, one of my favorite tracks has a very low tenor sax line that is much weaker than you hear with the Polks and low tenor is right at 100hz. You probabaly wouldn't even notice it if you weren't intimately familiar with the track. I'm just guessing but it might be useful if the PT's had a variable x-over control.
Right now I think I'd be very happy with them but I'm thinking about swapping them for a pair of 533-T's plus a separate sub (thinking about the S-10, S-12 or other sub). The frequency response curves for the T's is noticiably flatter, probably because of the two mid-range drivers vice one, and I'd also have much more flexibility in placing the sub. I'm not sure about this yet though.