I have to say... Be careful going down the DPC Latency rat-hole. A simple circle buffer (which both Windows and MC implement) should make DPC Latency completely irrelevant.
To be clear: I've seen similar stuttering when playing high-bitrate files back in ROHQ on my HTPC (which is an Intel Core 2 Quad Q9550 @ 3.5GHz). The CPU just can't quite handle it. Of course, the same files play fine for me on that machine in ROST mode.
I'm not sure what you are using there, but it could be CPU performance. Of course, if playing the file back locally fixes it, then that indicates that your network is probably flaking out (but not necessarily, maybe your CPU is so overworked that it can't handle the 5-10% extra load required to drive the network stack that hard). If you are trying to do something crazy like play back a 20mbps H264 compressed MKV on an Atom while pulling the data from the network? Yeah, your problem is that you are just CPU-bound.
In the real world? I'd be suspicious of your cabling or your Router/Gateway/Switch before anything else. Gigabit Ethernet should be able to sustain around 800mbps (100 MB per second) in a transfer pulled from a sufficiently fast source. If it can't it is usually:
1. Bad cabling causing unacceptably high error rates.
2. The Router or Switch might be flaky.
3. The drive the data is being pulled from can't sustain adequate speed (failing, fragmented, bad cabling, or on a "bad" bus like USB).
4. The network stack in Windows is buggered (spyware, bad drivers, etc).
I'd suspect things in roughly that order.
Other stuff can maybe cover up these problems, but the root cause is almost certainly one of those.
