Good morning, MrBoat. Hope the world is treating you well. I'm not familiar with the iNuke, so I can't offer any specific guidance, other than it has everything you might need. I wouldn't worry too much about diving too deep into the iNuke's dsp capability until you have assessed the situation more carefully using REW, Omnimic, or similar.
You only need to use the low pass filter in the iNuke if you have the speakers set to "large" (or whatever full range is in Denon parlance). In this case, set the iNuke's lpf where the Tempests roll off, 40-45 hz or so.
If, on the other hand, you have the speakers set to "small" then use the lpf of the Denon, rather than in the iNuke. Whatever you do, don't run lpf in both the Denon and iNuke simultaneously. I don't know how flexible your Denon is as far as choosing hp/lp filter frequencies, but even if it only offers a single choice (likely 80 hz) that's fine.
The first method is simpler to do, but since you were gifted a Denon with bass management, I encourage you to use it.
Be sure to peruse the subwoofer setup and calibration articles in the Home Theater Setup tab on the Audioholics main page. I seem to remember a helpful one that uses you favorite Jaco or Victor Wooten tracks rather than REW to dial in your sub, although doing measurements can really expedite the process. The rta gear would also help identify issues that your iNuke's PEQ can help fix.