To be totally honest I never got the buttkicker (but looked at it seriously) and decided to do a diy job with a bass shaker amp, speaker wires, a second sound card, a 50w bass shaker, and SRS software. I attached this to the PC table and it is quite immersive but slightly limited with just one bass shaker. This is why I was interested in the SRS shake kit which has 4 bass shakers (6 for the more expensive version) which you then put on your seat to give even more immersion. I suppose though if I wanted I could just attach a second transducer to the PC chair and connect it up to my existing amp which is powerful enough for two bass shakers. There are loads of possibilities and it is quite fun thinking them through. My knowledge of electrics was pretty limited tbh and I had to do quite a bit of reading before deciding which amp, transducer, sound card and software to buy and then how best to connect it all up. The advantage of a diy job rather than an all-in-one is that if any of my components goes bust I know how to replace them.
I suppose if you wanted you could get a second buttkicker and do a similar thing. Attach one to the PC table and another one to the PC chair. Not sure if you would need another sound card to be honest but I think you can get them pretty cheap.
I find bass shakers add quite a lot to immersion and are great fun. Hope you have fun too