Finally broke down and did it - I ordered a Dune HD Smart H1 from Duneplayer.com. Talked to Mike who answered some questions for me and was very helpful. Shipping was quick - it arrived the next day!
Hooking it up was simple. Getting it working took a few minutes, with a bit of my usual cussing. At first it was at the wrong resolution, and my TV was showing an improper resolution message. I don't know what the default resolution is. I had to press the mode button, then press a resolution mode button, 5 for 1080P. You also have to wait for a few seconds before that happens, but once I did everything in the proper sequence and waited it popped into place.
Next, getting it to see the shares on my PC took some more work. I could see my workgroup, I could see the Windows 7 Pro PC, but no shares would show up when I drilled down. Spent some time fooling around to no avail. Finally I set up a network folder on the Dune, entering the PC IP address and the share name. After a second the folder showed up and all my video folders were available. I saw some posts saying that the network browser is a little wonky. Not sure if it's an issue with the way my share are setup. IMO Windows 7 sharing is totally goofy and a big step backwards in ease and usability.
The interface was simple, just a list of folders\files, but it was very fast to scroll\page down, especially compared to my ATV 2 and 3. When I selected an MKV, playback was very fast to start. Quality was simply amazing, I was blown away! 1080P was great and the audio was fantastic passing through my AVR.  I selected bitstream for audio, but not sure what other changes to make.
It looks like my ATV's may be for sale. I may keep them just for music or Netflix, but I'll see what the Dune can do for me there. Now I need to look into Zappitti, and find a more detailed user guide.
Quite impressed so far.