Using my Open DRC-AN unit from mini dsp. I add a low shelf filter at 50hz of 4.5db and a Q of 1.0. This is personal taste and can be shifted. I also have my Submersives in PGM1 and change to PGM 2 after Audyssey which gives a 3db bump below about 45hz. So my shelf ends up around 9db rise at 30hz. After the shelf filter is set I take my raw response then apply cutting only to get as flat as possible. It is important to cut only as applying peak boost filters in nulls will only make very negative effects in the time domain measurements which in reality tell a lot more about our sound then a basic FR response. In REW we see this with the Waterfall and Spectrogram measurements. I actually do add a 15hz 4db boost to get flat but my thinking is down that low you would need 7ft deep pink fluffy bass traps to have an effect and I will never do so what the heck...My time decay, or any of us, down that low will never look good. No big deal. After I have applied the low shelf filter and the peak cut filters I run Audyssey and it flattens out even more. Very flat for me at this point. I then switch the Submersives to PGM 2, un-bypass the low shelf filter (You want to bypass before running Audyssey or it will try and flatten it out). And you are done! Without the PGM feature on the Submersives one can simply ad a couple more db to the low shelf filter.
It has been recommended to me to apply an LT down low witch cab be done in the advanced bi quad settings and filters but I know nothing about that yet.