Memory playback worse than disk... Why?

Hi,

I'm used foobar, now jriver to connect my new toshiba portege r830 (i5,4g ram, windows 7 64-bit) to my Dac via USB

I play 24/96 flac files, stored on a buffalo nas.

To even get close to near absent jitter, I use wasapi event mode (better than ks, wasapi,...), exclusive mode for Dac, and clear the buffer before each track. I also increased the priority if the jriver process.

When I elect to playback my files from memory (file uploaded prior to playback), I get these big crackling noises upfront, and experience more jitter than by playing direct from the nas disk. Why?

Poor laptop design, windows design, settings ?

P.s. I'm amazed how complex it has been to make 24/96 work (and it's still not perfect).