I have a similar setup to what you are going to be using. I have an MSB Gold Link III with powerbase, an M-Audio Audiophile USB, and an XP laptop. I use USB from laptop to the maudio, then into a Meridian 518 digital processor, which feeds the dac. The sound is decent, but not quite as good as a meridian 500 transport into the same 518. I'm guessing that the maudio is the weak point in the chain. You can get a used 518 for around $500 here, and it does a lot more than just dejittering. I use an audioquest vdm-5 from the maudio, and an MIT aes/ebu from the 518 into the msb dac. It certainly sounds a lot cleaner and tighter with the 518 in the mix.
I would recommend using foobar as a player and bypassing kmixer by using maudio ASIO, or disabling kmixer altogether. I've found that WMP does not sound nearly as good as foobar, unless you're using vista. I've also tried this combo with the msb digital director dejitter device, but the 518 sounds better and is more flexible.
