Vandersteen Sub woofers v Rythmik Subs


I really love the idea of the Vandersteen Subs where they are connected with the mains via extra speaker cable off right and left channels off the main amplifier, which is supposed to provide better bass transition from the mains while keeping the signature from the main amplifier. My question is with Vandersteen coming out with the SUB THREE and the price going significantly higher, I was wondering if there are other subs for less that you could integrate in the same way. (Most subs seem to rely on the line level input which is just a sub-woofer RCA going from the pre-amp to the amp on the sub). Can this same Vandersteen set-up be achieved with other subs?
I picked Rythmik since they are known (in the home theater community anyway) for being one of the best bang for the buck subs and the most "musical" of the bunch. (between Hsu, SVS, PSA).
And could I possibly achieve even greater sub-woofer nirvana since I could get an 18" for around $1500? Vandies only have 3 eight inchers.

I am a Vandersteen fanboy and I would like to support RV whenever I can, but don’t know much about my other sub-woofer options so looking for some feedback. Doesn’t even have to be related to Rythmik necessarily. If you know of other subs that can integrate the same way I want to know about it!

Thanks
bstatmeister
I guess I am confused about the differences in the way you configure the Rythmik via the speaker binding posts compared with the way the Vandy does it. I know you have to put in an analog high pass filter between the amp and the preamp in order for the bass to be correct once it gets to the vandy. Can you do this with the Rythmiks, as well? Or do you just send the full signal in? if you do send the full signal in is it proceeded digitally in the on-board amp? I guess I am still fuzzy on the filtering/signal processing options and what the pluses and minus’s are for the different types.
With the Vandersteen method the high pass filter goes between the preamp and amp so the signal from the speaker terminals is already filtered.  Whether you run the Rythmik's from the preamp's outputs or the speaker terminals the signal is passing to the mains full range and you use the crossover in the subs to limit the signal it sees.  You can buy aftermarket in-line filters to mimic the Vandersteen effect if you choose. Harrison Labs FMOD's are the most common.  Never tried it that way so can't tell you how it would sound.  In both of my systems I am running the mains full range and crossing in the Rythmik subs at the bottom limits of their frequency range.  
I am the other distributed bass user that Noble mentioned . I use 4 REL Q201e subs in my room . The front subs are under the main speakers a set of Ohm Walsh 2.2000 sat. I use a high pass cap in my tube mono blocks to pass 50 hz and up . I take the sub signal from the amps and send them to a passive volume control to set the gain structure to my DSPeaker antimode 2.0. From the DSP witch functions as a crossover and room correction device  the DSP has 4 outs 2 XLR and 2 single ended . the front subs run passive and use a crown XLS 2502 amp  .The rear subs use the internal plate amps set to LFE witch bypasses the subs crossover network . With this setup I have full control of the bass volume and crossover through the DSPeaker while  using the high level signal .     
@enginedr1960 - So, if I read your last post correctly, you compensate for roll-off below 50Hz with the passive pre? Does it have enough gain for this purpose? I guess that is possible if it is a transformer based volume control, but I thought passive volune controls were mostly attenuators. Or, perhaps the DSPeaker is where you get your subwoofer signal gain from? Please ’splain it to me.
One thing I have not seen mentioned yet is that the Vandersteen 2wq/M5hp system actually improves the sound of the main speakers by relieving them of the job of producing deep bass. The rest of the spectrum is cleaner sounding. It really makes a big difference. I run the Vandersteen 3a signature's with two (stereo) 2wq's and it is a very satisfying full range experience.