Help with whole house DVR and OTA tuner

A HTPC is probably your only option; none of the subscription-free DVRs have enough networking functions to let you stream recordings directly to other TV sets. Your only option would be to purchase separate DVRs for each TV, the benefit of which being that you'd have six tuners, although the programs you wanted to watch would still be tied to the DVR/TV pair used to record them.

The TViX 6620 could theoretically let you stream video from one TViX to another if you had a unit attached to each TV, but I highly doubt the performance you'd receive would be "wife-friendly". Even a HTPC with Xbox extenders (which I gather is the most elegant solution from reading posts here) might not meet that criterion.

This is pretty much spot on on what you'll need to accomplish what you asking. I agree with use WMC, but for OTA signal, it's not the only game in town. XBMC is probably a good alternative, but may be rough around the edges at this point.

If you're using WMC, it going to come with Windows 7, except W7 Basic. I assuming you have a copy of W7 Home or better. Microsoft included the license fees and EPG subscriptions with the OS license fee. It's just a one time cost. The longer you use it, the lower the cost gets. You can also go Windows 8, but the WMC is a $10 fee. I don't know if that is one machine license or multiple. But it's a one time fee, and includes the EPG.

You'll have a bit more choices in extenders since you're planning on just OTA programming, so you won't have to worry about copy-once tag. Overall, the 360 may be your easiest option to setup. It's just not that great of option if you ever plan to stream your media to it.

The number of tuners can be important. You need a tuner for every DVR or Live stream you may do at a particular moment. To watch one program while recording another, you need at least two. If you're watching one program and recording three, you'll need four. Just recording two, you need two. Thus, depending on how you plan to watch is going to have an effect. Obviously, if you only watch live TV with the build tuner in the TV, then it's just about how many shows you might record at the same time. Luckily, tuners without cablecard inputs are significant cheaper. I think you can pick up HDHomeruns for $50 to $100, which depending on the model, will have either two or three tuners. If you go HDHomerun, I would suggest the HDHR3. It has three tuners, and much more forgiving and signal strength.

I noticed would like the extenders to be able stream network files. Unfortunately, there are compromises that will need to be made. Althought, XBMC may be your best all around option. They have added DVR/Live TV to it fairly recently. They have a few set top boxes options, such as the Rasphberry Pi. And will be able to handle Netflix, Hulu, and so forth.

Otherwise, WMC uses a quirky WTV file format that isn't very popular in a lot of media devices. You'll have to take into account the file formats that the STB can accept. The 360, which works well as a media extender for WMC, has a narrow file format it accepts. The PS3 is better, but doesn't work well with WMC.

Personally, I used Roku boxes. It works well for online streaming serivces such as Netflix, Hulu, Crackle, and so forth. It's relatively cheap. I use Plex, which is similar to XBMC. Plex can play WTV files; non that are copyonce flags. The problem, fast forward and rewind is hit and miss. Skip forward and rewind work better, but it sometimes crashes; doesn't work well on mobile devices. The Plex Media Server will run on your PC, but it will transcode the file to something Roku can accept, which is what happens for the WTV files. A nice bonus to Plex, it's relative easy to setup, and can stream to mobile devices will relative ease. Nice for content consumption away from home. Heck, I streamed a program that I DVRed, that is only available in my home market, while at friend's house, that is five hundred miles away. Although, I've never really been impressed with Plex's Netflix and Hulu integration.

Try the PC forum since those are not "DVR's" in spite of the ability to record a TV broadcast;
http://www.avsforum.com/f/26/home-theater-computers
http://www.avsforum.com/f/39/networking-media-servers-content-streaming

WMC addresses all of your bullet points and might be the best DVR for your needs. If you follow my signature link you can see how it all shakes out... at least has for me. However later on you mention using only a PC and Roku... you would need a WMC extender (or another PC - not as elegant) for additional displays.