So, I started with what you had, but came to a slightly different answer than yours. Part of this is because you are using a DSP which utilizes 2x adau1701. As such, you can instead use Linkwitz-Riley filters, which is a cascading butterworth second order (so two second order butterworth with the same values being applied to both butterworth). This has phase benefits over butterworth.
Now, as for the entering of the information for the driver, here is what I have:
Now overall your system looks good, but at that price, you might consider looking for a DSP with either an ADSP-21489 (like miniDSP HD 2×4) or with an ADAU1467. Even with 2x ADAU1701, it just seems for the price that there may be a better solution for your needs, so long as only one device will be hooked up to it. If you are hooking up the sub with other speakers going to the DSP, then it might be understandable. But generally, if just this device, then something else may be a better buy.
Let me know what you think of this design. This does cause the length of the port and height to increase slightly, but it also allows for up to 250W before reaching excursion, thereby making the driver louder than your current design (even if likely only a dB or so).