The delta is a great woofer, especially factoring in cost. Since you have a Scan-Speak 8" we share a similar reference. I will say that the delta sounds similar at low volumes, and they both have a full midbass when up against a wall or corner. but since the delta is so much bigger and has to move so little even at high volumes, the phrase that comes to mind is effortless slam. The 8's that I have are the stiff paper woofers so they break up terribly in the mids. It is impossible to compare the two above 500 Hz as the deltas sound great even at crossover. Oh! and believe it or not, the delta is only about 50 % heavier.(not bad when you are 4 times bigger) If I had your sub I might aim for something with less bass than a delta, something more for high output midbass/midrange.

The omega still looks good for you, but I understand about the cost. The woofer you spec'd in another post also looks real strong, but I can't see how they get it in a box larger than 2 cubic feet.(as per BoxPlot) It looks like a great driver to use with your sub crossed around 60 to 90Hz, because it starts rolling off fast at 50 Hz. It looks to be a real high power midbass, and it does seem similar to an omega 15, but lower Q and higher gauss (not a bad thing). Thats a big bad motor. It looks good in a small box too, 2 cubic feet and a port 4" by 3.5" long.

Does Eighteen Sound make a hot 15" with similar specs, but without the double spider? That adds a lot of moving mass and is likely the reason they say to cross at 800. (mass rolloff) Might save you some money too. It isn't really necessary for midbass duty unless you will really pound these things HARD. If your compression driver can do 800 or 1000, it might be ok though. It does appear from the specs and the presence of copper shorting rings that they are doing quality stuff. (just a guess since I havent ever even seen or heard one, but makes sense) If you get the double spider ones, break them in like you are trying to blow them up! I use to sell some double spider car woofers, and most of the customers amps were not capable of moving all that spring tension real well. (I was the service guy so It became my problem, 1 hour on the 1200 watt mono block usually freed them right up)

As for break-up on big drivers, it varies a lot. All drivers break up, It's just where and how bad. Paper is usually friendly and it generally sounds even better than it measures. If you were using kevlar, carbon or glass you would want to cross an 8" about 1000Hz 3rd order. any higher and you would need a notch filter also. Paper self damping, and some drivers like the omega do not show ragged or rising response before mass rolloff. I am not saying that it doesn't have break up, but it has a strong motor and it doesn't have spikey or rising response above 1000Hz (or anwhere else for that matter). How often do you see that? Thats got to tell you something. It seems very controlled in all of the usual behaviors. It's a shame about trade laws and tariffs really. It appears you will have good parts from Eighteen Sound though.

P.S. If you find more info online (graphs, pictures) for eighteen sound let me know. I am not getting much from what I have found.

P.P.S. Take all the Omega stuff with a grain of salt. I have the hots for them right now, and I do not even own any yet. You must admit they have insanely well behaved frequency response in the crossover area compared to just about anything else period.

Let me know how it goes,
Thomas