YES! Get the 540! It has a mode where it will fire it's IR focus-assist beam but NOT the flash. I've used this feature when I am going non-flash with my 50mm f/1.4 (folks go "hey, the flash didn't fire!") Of course, if you are using the flash as "flash" , the IR beam will aid in AF as well. Don't think my old Sigma EF-500 Super had this AF-assist/no-flash mode.
Oh, regarding the "info from 540 flash", I believe the K10D just sends a "it's dark, fire the IR beam" message to the flash, and that's it. The beam will hopefully "light up" the subject enough for the AF to work. BTW, I've used this in complete darkness and it works! And the picture actually comes out decent. Did I say you need to buy the 540
Yeah, the "flash-pulse-of-death-as-AF-assist" is kinda awful if you ask me. Unfortunately, when I use the built-in flash to trigger my 540 wirelessly, it uses the built-in for AF assist, rather than the off-camera 540
Time to get another 540 or some hotshoe cables.