Subwoofer boom is too much for me...

1) Auralex Lenrd bass traps from floor to ceiling in the corners of front wall (see pic in my virtual system)

2) An isoacoustics or ASC stand for your sub 

3) The DSPeaker 8033 sub eq device

This has worked for me every time I've set up a sub, whether it be REL or another brand. The idea of keeping the crossover as low as possible while volume high was tough to swallow at first, but now makes sense. 

Subwoofer tuning

And yes, I have bass traps and such. 

Something like this is better. Available in most size.

 

less likely your port is the problem and more likely you have incorrect slope and x-over frequency relative to your main speakers. fixable to a certain extent. 

Mikeydee: Sure plug the bung hole. Let us know it it works on your subs.