Jason,
I capture from a Sony DVW A500 through SDI and use the Stealth serial adaptor that came with the CineWave card. It has worked great from the beginning in OS9 and now in OSX (with the updated driver from the GeeThree site) One thing to be careful of, though, is to get the right cable. A standard Mac 8 pin DIN to 9 pin serial WON'T WORK. You need a cable that has the proper pin configuration for Sony RS-422 protocol. I got mine here:
http://64.227.162.236/miva/merchant.mv?Screen=PROD&Store_Code=imagineproduc...
If this link doesn't work, go to imagineproducts.com and click on "cables" in their online store.
Best of luck.
Kirk