Ok, after my frustrating experience of a couple of nights ago I've managed to learn a few things. The things I discovered concerning WPS and turning SSID off may work differently with different hardware though, so YMMV...
With the WNDR4000 and the TiVo Wireless-N Adapter, WPS will only work if SSID is turned "On" when you attempt to auto-configure. Every attempt I made with WPS while SSID was "Off" resulted in failure.
I never did confirm whether or not WNDR4000 and the TiVo Adapter would successfully auto-configure the 5Ghz network while the 2.4Ghz network was enabled. I ended up just turning off the 2.4Ghz side while the WPS was doing it's thing.
AFTER the TiVo Adapters were successfully configured and in operation, turning "Off" the SSID on the 5Ghz network to which they were configured had no detrimental affect on the TiVo's. Everything still worked as planned. Again, the reason I wanted to turn SSID off was because of comments I had seen in a NetGear manual (and elsewhere also) about other wireless devices sometimes "pinging" networks that were broadcasting their SSID, and causing the network speed to drop.
So I'm now using the three TiVo's on the 5Ghz network with SSID turned off, and my other wireless devices don't even see or try to inadvertantly connect to that network. I have the 5Ghz transmitter turned on only
at the downstairs WNDR4000 which acts as a Wireless Access Point. [AES] encryption is used for that network.
The 2.4Ghz transmitters are turned on at both the downstairs and the upstairs WNDR4000's. This allows for good signal strength at the Wireless-G XBox and the wireless desktop computer located downstairs, and the two notebook computers that are used upstairs or downstairs at various times. "[TKIP] + [AES]" is enabled on the 2.4Ghz network since the Xbox and desktop wireless adapters don't support [AES] only.
So far since finishing up this afternoon everything seems to be working well, so I'm happy and the TiVo's appear happy.. no more stuttering during streaming. I'm running a transfer test right now to see how long it takes and what transfer speed I am getting to move a half-hour show from one DVR to another.
Bobsilver.... thanks for your help with this. Your comments and suggestions have proved to be very helpful in getting this to work the way I wanted it to work. Edit: My "test" transfer finished while I was typing this post. It took 11:10 and the transfer rate was 32.56 Mb/s according to the diagnostic screen on the TiVo. This was almost twice as fast as the best transfer I had seen before. Then I ran another test, this time copying an hour-long show from the other TiVo. This second test took 24:33 and the transfer rate was 40.26 Mb/s according to the TiVo diagnostic screen.