High pass filter need

Thanks for the suggestions. The JL sub doesn’t have high pass outs so not an option. The Harrison labs FMOD look easy enough to try. Heck, I work in Dayton. (Location of Parts Express)

i am more worried about over driving the C1 woofers than the DNA-2. Its a beast. 600 w per ch into 4ohms. So the port stuffing is also worth trying. 

You should check out this HSU high pass filter!
http://www.hsuresearch.com/products/high-pass-filter.html

To block highs from your main amp, at a specific chosen frequency, you have to know the amp’s input impedance, and choose the correct value of capacitor, to install in series with the input signal. The old Dahlquist DQ-LP1 passive/active crossovers used this method, in their high-pass section. In the Dahlquist manual(I’m providing the link), you’ll find a table(and formulas) that will help you determine what value of cap(and perhaps, resistor) is necessary, to meet your desired crossover point. Dahlquist used a 6dB/Oct slope, because higher orders cause phase shifts. These typically very small value/size components, can be easily installed either inside your preamp(at the outputs) or inside the amp(at the inputs). https://sites.google.com/site/mpbarney/home/dahlquist-dq-lp1 

If you are running your system balanced this works well:
Ashly XR-1001
https://www.amazon.com/Ashly-XR-1001-Crossover-Connection-Chassis/dp/B001UIQ1CM
I used one for a while before upgrading to the JL CR1 which has a slightly better feature set but at more than 10X the cost.

BTW, the Ashly has a jumper that you can remove to bypass the 20Hz hi pass (rumble) filter.