Is this how a Subwoofer Crossover is supposed to work?

I bought two Starke SW12 subwoofers that I installed.  So far I'm not particularly happy with them.  They are way too loud even with the volume set almost to off.  More importantly, I'm having trouble integrating them into my system and I'm wondering if that is because their crossover setting is really functioning as I understand a crossover should. Attached please find measurements from Room Equalization Wizard with SPL graphs of the two subs (no speakers) taken at my listening position with the crossover set at 50 Hz, 90 Hz, and 130 Hz. Ignore the peaks and dips which I assume are due to room nodes.  All of those settings appear to actually have the same crossover point of 50 Hz. All that changes is the slope of the rolloff in sound levels. This isn't how I thought a properly designed crossover was supposed to work.  I thought the frequency the levels would start to roll off would change, i.e. flat to 50 hz then a sharp drop, flat to 90 hz then a sharp drop, etc. etc..  But Starke says this is how a subwoofer crossover is supposed to work.
Any experts on here with an opinion about this?  Is it possible to buy an inexpensive active crossover that I could use in place of what is built into these subs?
LImited knowledge but I have used subs and feel I get some reward.  I have used successfully small cheap ones for computer, kitchen and better one's (REL) for main.  Some main speakers do better than others with sub.  My old KEF's are a bit slow in the bass and the sub can accentuate it.  Most of the time I find keeping the role of the sub subtle is better.  A touch of bottom, warmth, fullness but not a lot. My new speakers (Sonus Faber) are cleaner down to where they stop and I find that easier to get the bass in there improved without drawing attention to itself   Images again are bigger, deeper, fuller.  But the key for me is a light touch.  I agree with those that suggest one at a time.  Placement and settings very key  And in the end one setting might not give best results on ALL music I settle for the settings that provide SOME benefit but least annoyances.  
ONE possibility is that the subwoofer’s voice coil has very high inductance which results in significant peaking in the 40-50 Hz region,


I think your characterization, that this sub is rolling off far too soon is spot on, which is why I suggest removing confounds. :)
There is some great information here, but this thread REALLY has me wondering if I want to mess with subwoofers!
Sorry for all the conjecture. I see a decent amount of room interaction so I would do what Duke and Eric recommended. Measure close to the driver and just one sub at a time. I would put it in the middle of the room, as space permits, and measure with everything set to flat. The web page mentions a bass boost or "punch" setting? Make sure that is not engaged. And lastly, as has been mentioned, the XLR output is much hotter. Get a cheap 1-2 RCA splitter for both channels and start over. Best of luck and keep us updated.
   Sub Setup......One of the greatest challenges in audio. Some very good suggestions here. So many I can't imagine one trying all of them. Since your post asks about the crossover function of the subs I would address that first. Given your setup I have another suggestion......An active crossover. With that the sub's crossover is set to it's highest value. Then the active crossover selects the actual crossover. There are several brands. JL Audio makes an excellent one but a bit pricey. You may search for an Outlaw ICBM in the used market, since it's not in production anymore. Original cost was $250 so a used one can be had for a reasonable price. Offers hookup for 2 subs (and other speakers) with 2 different slope settings. Maybe worth a try?