Topher, You should be able to got to the logitech site and see if you can add an IR-543 as a device. If you can then it should control your dimmers fine through the IR-543.
If your 659 does support all 16 device codes once setup for the IR-543 then you can make a very crude controller using your 659 and the IR-543. This is very crude and I only suggest it if you are not intending to add any more X10 in the future.
First you setup an X10 controller device (or lamp device) in your 659 that will allow you to send all the device addresses required for setup commands, including device 16. The crude part is that you need to manually rotate the house code wheel on the IR543 to send the different house codes required for scene setup (M,N,O,P if I remember correctly). First you rotate the wheel on the IR543 and then press the device 16 key on your remote for each setup command in order. It is laborious.
I did this with my H880 and it worked fine. I only had two X-10 devices that needed scene programming. If I were to add more I would either buy a X10 controller or the IR-543-AH (all house codes would be another option). The IR-543-AH is much more expensive than the IR-543 however.