Is this how a Subwoofer Crossover is supposed to work?

@ OP
Check out ieLogical SubterraneanHomesickBlues for a little information on setting up subs and how their controls work.

Definitely characterize you subs individually at close range and in the same position.

Visit hunecke.de | Loudspeakers Calculator and input your room. Do the same in REW.

Sadly Starke doesn’t give any sensitivity for Bal/UnBal, or much of anything else. I couldn’t find a Willsenton R8 manual.

Using BAL to the Sub and RCA to the R8 will have about 14db more gain to the subs, assuming the DAC uses industry standard levels. If the DAC does not have a level control, the subs are being driven an unattenuated signal.

Note that the SW12 has an insufficient control set to integrate well except in possibly a single location.

Except for the name calling this has been an interesting thread. I've learned several things.

I realize that I'm not answering your question but I would like to take a step back and look at this from another angle.

1. Your Moabs are spec'd to 20 hz. I've never heard these speakers but they have great reviews and I've never heard anybody say they are shy in the bass.

2. You purchased two subwoofers which cost $350 each and weigh 40 lbs. to supplement the bass of a pair of full size, full range, highly regarded $4500 speakers that reportedly compete with speakers costing 10 times their price.

3. If the Moabs go anywhere near 20 hz you don't need subwoofers. If pipe organ is your favorite type of music and you are missing the 16hz notes then you could spend several thousand dollars on a sub that would not only go that deep but was equipped with a high quality crossover that included a very low cutoff point. Wilson makes a sub for $40,000 that accomplishes this purpose.

4. The subwoofers you bought are accentuating the frequencies that your Moabs are already putting out. They are doing nothing constructive.

5. If I understand correctly, the subs have no speaker input and no speaker output. In my experience cheap subs are usually designed so that you hook your speaker wires to the sub and the sub crossover sends the main speakers the high pass signal. That prevents the sub and the main speakers from doubling the bass frequencies. It looks like these subs are designed for folks who have small stand mounted speakers that have their own natural rolloff at 60 hz or higher. It's pretty obvious to me that they were never intended to integrate with a pair of full range speakers like the Moabs.

The lesson here is that your subwoofers are doing more harm than good. You are just adding low frequencies that your Moabs are already supplying. If they sound bass shy then it's likely that your room is the problem, not the speakers. It's probably not feasible to return the Sparkes but you should have devoted that money to room treatment instead of subs.

I can provide an example of a subwoofer/full range speaker setup that is working well. I have a pair of Thiel CS6 speakers that are rated to 28 hz on the low end. The bass is great but it is lacking in the lowest octave. I also have a 15" Velodyne subwoofer that incorporates a pretty steep crossover. It is adjustable down to 40 hz. I use the Velodyne with the crossover at its lowest setting. About 80% of the time the subwoofer just sits there looking impressive but not making any sound at all. But when I put on something that has low bass it gracefully adds the gut jiggling frequencies that the Thiels just can't reproduce. But this didn't just happen. I've spent a lot of hours on speakers placement to get there.

Sorry to be sarcastic, but if you think your Moabs need a pair of $350 subwoofers to sound good than you should seriously consider returning the Moabs, not the subs.

This is why I purchased two REL S2 SHO subwoofers.  They use a high level connection to make their subwoofers act as lower end subwoofers to extend the bass on the main speakers.  If you set things up correctly, you won't hear their subwoofers over take your main speakers.  I have the volume on my REL's set at about 40%.  They are smooth and seamless.  I wonder if REL has a patent on this technology?  If not, can't understand why other subwoofer manufactures aren't using this as well.  If you have not auditioned REL subwoofers you need to do so.  As with everything else, main speakers and subwoofers need to positioned correctly to receive the best sound. Be curious to hear what others in this group feel. 

For some reason I am not sure the make and model of both your main speakers and your subwoofers?  Can't imagine you can buy an audiophile subwoofer for that price range?

Hi 8th-note

I have to take some issue with your statements, as I don't think they are in evidence yet:

2. You purchased two subwoofers which cost $350 each and weigh 40 lbs. to supplement the bass of a pair of full size, full range, highly regarded $4500 speakers that reportedly compete with speakers costing 10 times their price.

I think you are far too focused on cost here. Admittedly, I'd have bought a Hsu or SVS, but integration is going to be a much more important step here than worrying about not spending enough money.

3. If the Moabs go anywhere near 20 hz you don't need subwoofers. If pipe organ is your favorite type of music and you are missing the 16hz notes then you could spend several thousand dollars on a sub that would not only go that deep but was equipped with a high quality crossover that included a very low cutoff point. Wilson makes a sub for $40,000 that accomplishes this purpose.

Woah, nope, totally disagree with this entire statement.  Subs bring a lot more to the table than a spec. The ability to relocate them, to equalize them, and to limit the bass required by your main amp and speakers are big deals.  Done perfectly, you bring a lot more power and dynamic range to the system than you would have otherwise, and reduction in distortion.  Also, this is a giant PITA to do well, as this thread will attest to.

4. The subwoofers you bought are accentuating the frequencies that your Moabs are already putting out. They are doing nothing constructive.

We have not seen evidence of this, yet. So far all we have see is the sub response, and that the sub is too loud.  However, yes, the future of this system should be correctly integrating the sub with the main speakers.  One step at a time.

OP:  I just noticed that your main speakers are ported.  I am going to suggest you plug them before attempting to integrate with the subs.