An HD Homerun by Silicone Dust, (or the Mac version by Elgato has an EyeTV app) does all this, but smoother, and features TWO television tuners. Oh, and costs even less. You use any PC on your network, (anywhere in the world), as your DVR and record in any format that you want.
DVR recordings on the PC/Mac can be streamed to any DLNA device, (Sony TVs, Sony Set-top Streaming devices, Xbox, Playstation, WD Media Center, etc). Or, you can easily stream the HD recorded video files with an AppleTV.
However, streaming recorded video files directly from your PC/Mac isn't currently supported by Roku.