2 subs can work very well but they're a pain to set up correctly. I think you'd be limited by the lowest quality subwoofer but a combination of the BK and SVS could work well with the BK supplying the mid-bass and the SVS tuned down to supply only the lowest frequencies (for example).
I would still prefer to use 2 identical subs to make setup easier though. It's also worth bearing in mind that with that much cash to spare it would really be a better idea to get a single much better sub than 2 of a lesser quality.

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