MMG sub hookup....

If you want to high pass to the speakers you can use this HSU high pass filter. If you want to run the speakers full range you will need Y adapters from preamp into amp and into the subwoofer!
I use this to high pass to main speakers!
You will need 2 pairs of Y adapters to do any of these choices!

http://www.hsuresearch.com/products/high-pass-filter.html

I’ve tried it both ways and I prefer using high pass to the speakers. Some prefer running full range. It all depends on the speakers that you are using. What sub are you using? I doubt that it has a high pass filter ! BTW, if you decide to go with the line level option these y adapters are what I use!

https://www.audioadvisor.com/prodinfo.asp?number=AQM22FHRD

You are not giving up anything. All you have to do is adjust the low pass filter to what sounds right to you. The Maggies go down to 40HZ so just fill in the bottom end!

The speaker out on that sub does not have high pass filter! Just run the speakers full range and see how you like it!