Kenny, I understand your confusion. The subs Salk Audio offers are the standard Rythmik sealed (either 12" or 15"). Jim Salk installs the same DIY kit you yourself can buy from Rythmik, and installs it in his own larger (4cu.ft. vs Rythmik’s 3cu.ft for the 15"), better braced, beautifully finished enclosure. The OB/Dipole sub is not offered by Salk, and is a completely different animal.
Before getting to the OB/Dipole though, yes, you can try out any of the Rythmik subs (for 30 days I believe, but don’t quote me), paying only for shipping if you send them back. They offer a bunch of different models, both sealed and ported, with 8", 12", 15", and soon, 18" woofers. Also a number of different plate amps, with different power ratings and control features. What they all have in common is the Rythmik patented Direct Servo Feedback design of owner Brian Ding.
The OB/Dipole sub is a joint venture by Rythmik and Danny Richie of GR Research. Danny was already designing OB speakers, and when he learned of the Rythmik design, he envisioned the mating of it with a dipole sub, and contacted Brian. They put their heads together, and co-designed the OB/Dipole sub.
The sub is not available as a ready-built, try-it-before-you-buy-it product, but only as a DIY kit. Don’t let that scare you away---there is a fairly easy way around that. You can see the kit listed on the Rythmik website, on the DIY/Kit page. It consists of the Rythmik A370 plate amp and a pair of 12" Open Baffle woofers, for one channel---two kits required for a stereo pair obviously.
But Brian does not actively promote the OB sub, Danny does. I have suggested to Danny that he make a listing for the OB/Dipole Sub kit on the GR Research site, but he hasn’t gotten around to it yet. You can find information on it buried in the listing for the 12" woofer in the "Drivers" section of his product listings.
But where you really want to go to read about the sub is on the AudioCircle GR Research Forum, where there are several threads discussing the OB/Dipole sub, with pictures posted by those who have made them. It is also there you will find the makers of the H-Frame that the kit is installed in. The frame is offered as a flat pack, and is not much harder to assemble than Ikea furniture. Anyone not wanting to have to do that could have a cabinet maker assemble it in a couple of hours, then paint or veneer the MDF (1.5" thick!) it is made of.
Check it out, it’s really special. The OB/Dipole sub has been incorporated into several full-range speakers, among them The GR Research Super-V (which was awarded "Best Bass at the Show" for several years at RMAF) and Serenity Acoustics Super 7.