Hi KJ,
I've not read anything that would indicate that Dolby or DTS processing reduces the LFE signal by half if the fronts are set to large and the subwoofer is set to "none". I suppose it would make sense if they did, since LFE signals themselves are generally too hot to send to typical main speakers. The reason a stand alone sub is suggested for home theater is that most speakers don't have the the power necessary necessary to produce the extremely loud LFE information (which is often mixed 10 db higher than the stereo bass that appears in your mains). All that said, some A/V controllers (and possibly receivers) have a bass limiter that will cap the LFE output so that you don't get distorted bass through your mains.
Of course, MOST people's front left and right speakers don't have subwoofers with their own amplifiers built in. I ran an experiment once a couple of years ago where I turned my sub's power switch off and listened to a movie track with just my PTs. Once I had that reference, I went into my receiver and turned the subwoofer to "none" I then played the same movie track and, wouldn't you know it, there was a LOT more bass than before.
So, I know that the LFE track is getting sent to the mains, but whether it is reduced or capped off by your A/V receiver I'm still uncertain on.
The bottom line is that, while you will often get more even bass by using the powered towers, you won't get some of the super LOW bass that an s-10 or s-12 could produce. The 8" subs in their enclosures are powerful and capable of being quite loud, but just don't get down to 20 or 25hz with the same gusto as a 10" sub or larger will.
This is why I suggested the 533-T and stand alone sub. OR you can use the PTs AND a stand alone sub for serious, serious bass. I just think the former makes a better value for a room of your type.
Caleb Denison