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
Yep 1/4" inch mic/headphone plug same thing as a TS plug (I think TS is used more in the pro audio world) and my amp is a pro audio amp. It's a behringer EP2500, it's got a lot of power and was inexpensive so that's why I bought it. It was pretty loud when I first got it due to the on board cooling fan that sounded like a jet turbine, so I did the fan mod and now it's very very quiet. I remember I bought it with the samson s-convert since it didn't accept RCAs but it did take XLR. I thought at the time that I could benefit from the balanced connections, but I've never done a direct comparison between the XLR and the TS. I just bought those plugs from Amazon, so I will let you know how the comparison turns out.
If the TS connections sound better than the XLR with the Samson (which is the hope since I will be removing additional stuff) I will be a happy camper since the unbalanced Vandersteen cross-overs are significantly cheaper if I'm not mistaken. (Honestly I would rather buy an extra sub than a cross over - at least to start off with...lol)
Nope, the balanced and unbalanced M5-HP crossovers are basically the same price (approx $700 used). The fixed crossovers are much cheaper (say $250).
In my opinion, using balanced connectors would be the best way to go as cable length and composition make less contribution to the sound performance.(Don't take my word for it, PM Ralph at atmasphere).
Bob
BTW if anyone knows someone who could use 100k  X-1 crossovers I will send them for free as I have the M5-HP.  
@noble100 and others interested in room acoustics: which other fora are you active in?

I'm interested in discussing and posting some measurements (which Agon doesn't allow) and would live to engage others who share that interest.

Cheers!