I use the Buttkicker and while it WORKS in AFS2 (using audio rather then USB input) it is very subdued due to the minimal range of audio spectrum generated by AFS2. Works MUCH better with X-plane and DCS!
I use BK, with a dedicated amplifier, and I can shake the chair pretty well. I can also filter the bandwidth and I don't think there is any spectrum issue. Yes sound channel is not the same as if we had a motion channel, but still it works pretty well. Now if I could get the audio in the rift and the BK at the same time without using some 3rd party crap software, that would be ideal.
Incidentally I only fly stuff that makes noise (jet, helo, F4U, etc..), no surprise airliner don't shake much, that would be the point usually.