Build 155 is pretty much the same as earlier editions with respect to Firewire/1394 issues.
1. WASAPI output via 1394 is unusable because of pops, 15-20 a minute. Yuck. This happens with WMA 96/24 lossless as well as WAV files.
Using WMP, also using1394, zero pops or tick, but the sound is altered (euphonically) via the Vista audio DSP stack. Buffering times from 50 ms to 5 seconds don't seem to influence the results. So WASAPI doesn't like going out via 1394; WMP is fine with it. Does this give any clues? It's the same 1394 driver, just being fed via WMP rather than WASAPI.
System configuration is Toshiba Qosmio 1394 to M-Audio, SPDIF out to Lavry DA-11.
2. WASAPI output via TOSLINK is free from obvious artifacts, just doesn't offer the same overall sound quality that SPDIF does.
System configuation is Toshiba Qosmio TOSLINK via Wireworld glass optical fiber to Lavry DA-11.
It looks like high-end USB to SPDIF, and 1394 to AES, SPDIF converters will be in house shortly... Standby