which output setting sounds best?

^^^^ ditto ^^^^

I don't think it matters. You are not getting anywhere near a decent signal with the USB/HRT. It is all veiled anyway. Doubt you will hear a difference.

I have been using a Wyred4Sound Dac2 which is asynchronous. Also using J Rivers 16 with Vista. Wyred4 sound recommends Kernel Streaming, but I have switched numerous times back and forth between KS and Wasapi Event with almost no perceivable difference. I have noticed a bit of a shift in imaging from left to right with Wasapi Event seeming more centered.

Give them all a try. Its an easy experiment.

Windows Audio Session API (WASAPI) is the Windows-resident interface provided in Vista and later OS versions that supports exclusive bit-streaming to a specified device in native resolutions up to 24/96 via USB 2.0.

There are likey other issues with Vista 64 that may lead you to want an upgrade to Windows 7. But WASAPI should be resident and if so,

This is definitely the selection of choice - unless your DAC supports higher resolutions, e.g. 24/192 or otherwise directs you to another driver.

Media Center includes WASAPI as a standard option. Run WASAPI in Event Mode if possible (In some cases you may need to increase buffer size from the default of 50ms).
This allows your DAC to impose control of packet timing and size.

BTW, Media Center's core algorithms take full advantage of 64-bit mode when available.

Good Luck.

Most of the posters are correct, but I take exception to Cerrot's position. Upon inspection of your virtual systems, I can see that in your eyes and budget, the HRT may seem "indecent", but to someone just breaking into PC Audio, it's a real drag to hear that their chosen device is pretty much worthless. The HRT can certainly be bested by other products, but it has been well-reviewed at its price point and would be a perfect place to start for someone just testing the waters with PC Audio.

Saying what you did without offering advice is akin to telling a kid you won't teach him how to swing because he's "a little short for baseball". It's not about the gear, it's about enjoying the hobby along with enjoying the music.

Evan