I tried directsound and I got a latency around 200 ms. I retested waveout and I got a latency around 170 ms. It looks like waveout is slightly faster.
cpu usage monitoring I think you'll like this tool for monitoring cpu usage of single processes. http://www.sysinternals.com/Utilities/ProcessExplorer.html Right click on a process, select 'properties' and the 'performance graph' tab.
I think I was wrong when I said that. The CRC information is not dropped. It's sent with the AC3 data. I suppose decoders/receivers use it.