How to choose monitors?

[Tomer=Trance]

how low do they go that you want to get a sub to cover the whole lower sonic range?

[flexoffset]

how long do they get that you want to get a sub to cover the whole lower sonic range?

I'm looking at a sub more or less for visitor-shock-value. These ADAMs have such tight bass that it will probably not impress visitors (I'm breaking into advertising/corporate presentations).
I figure a sub can 'help' out in order to 'show off' the presentations if I have a bit deeper low end. The ADAMs get plenty low, it's such an extremely accurate low with no added harmonics that it takes a bit of acclimation.

Of course, this may change once I get them set up in their final resting place. I'm out of money right now, so it will be a while.
The group I tested in was a 5.1 setup and had a sub (M&K 5420 ?) underneath the mixer and it kinda filled out the deep bottom ... probably even over-hyped it just a touch.

The S3A supposedly go down to 35Hz but I begin rolling everything off at 40Hz around 6dB to 12dB anyway. I'd like the sub to kind of lightly 'feather in' at the bottom range and when I have visitors, I'll crank it to taste to impress.

Sometimes I just like to crank stuff and feel the earth shake under me (in a non-earthquake way).