I tried this, and at least for me, it works fantastically well.
I say "at least for me" because Opus warns that this may not work well depending on your sound card.
Their solution is to suggest the Creative SoundBlaster USB "sound card" for $25. Not that bad when you consider what a huge improvement it makes to the ButtKicker.

OPUS THE BUTTKICKER!
This is so exciting, I hardly know where to start!
First off. If you have a ButtKicker, download the BETA copy of OpusFSX. Read the OpusFSX Beta ButtKicker Audio Control manual.

If I remember correctly OpusFSX is only a demo in the sense that it's time limited to a half hour at a time. It's not feature limited, so you can play around with it quite a bit.
Now if you DON'T have a ButtKicker, you're in deep dodo. You're going to have to return all your , ummm.... All your Year End presents (see how I cleverly got around the Merry "C" word).
Y'up. Get them all together and return them to the stores so you have money to buy a ButtKicker. Be creative if you have to... Got any organs that you don't REALLY need?
So just what does this do?
It lets you send certain frequencies down the wire to the ButtKicker. For the most part you can modify the frequencies, volume, and often the duration of different FSX events such as the landing gear going up/down.
How good is it?
Remember THIS IS A DEMO built into their main software.
Again, How good is it?
With my eyes closed and the plane slowly rolling along I can feel the difference between the runway and the ground.
They do warn that your sound card may have limitations and they recommend buying the Creative Soundblaster X-Fi Go! Pro USB Audio System.

It would probably be better to show you a few pictures, than to tell you that my butt's buzzing.

This is the main Opus screen. Once you have Opus set up and working click on Configure.

Next click on Enable ButtKicker Audio Control

This is a rather interesting bit, YOU CAN COTROL THREE (3) BUTTKICKERS! Is anyone rigged up for a co-pilot?


This is also where you might find a problem. I had 3 choices for the speaker system to use. Only one worked, but it worked VERY well.

When I bought my ButtKicker I thought that individual events in FSX would cause the ButtKicker to respond. Didn't happen.
BUT NOW YOU CAN TUNE THE OUTPUT OF FSX!
Overall it works VERY well, but they do warn people that it's still a work in progress.
And most of the problems have to do with this being tied to the FSX internals. The only big problem that I noticed was that the sound/feel of the landing gear going up/down is off. But they're working on that.
Remember: These ARE NOT sounds added to the ButtKicker. These are event driven sounds passed to the ButtKicker.

Consider the Opus software as an essential part of the ButtKicker.
Bur it's also the best FSX weather system that I've found.