Since this amp is sold, some comments about these amps...
The Crown K series is the bomb for a sub amp. It has no fans! It also is a bit more beefy that most plate amps. Nowadays there are a number of sub eq and xo options that are inexpensive and effective. Our own Kevin @ DIY cable offers the woofer widget. I am not 100% sure all the features and how it works as I have a Behringer feedback destroyer for that purpose, but seems like a good and user friendly solution (the behr has a steep learning curve, but cheap and effective).
I look at pro audio amps as the best long term sub solution. You can change your subs without having to change over all the hardware with it. PA amps should easily outperform a plate amp and are much more bullet proof.
Christof's sub boxes are something quite unique and special, which is another point in favor in doing the seperated solution. Plus, when you put it all together yourself you are more inclined to spend the money on a better driver which makes a big difference.
Just points to consider when sub shopping.
Good luck!