Thanks for replying.
I never get an option to configure the tuners separately, but perhaps it's related to the fact that WMC doesn't seem to be able to get signal strength data from the second tuner (a Hauppauge HVR-950).
On the Digital TV Detection Result screen after setting up 1 ATSC tuner, it says that other tuners or TV signals were detected but will not be configured. The details screen shows that it's the 950 not being configured and that it thinks there's no TV signal for it. To include it, I have to choose More Options>Configure manually, where I see a checkbox for each tuner. Then when I go into the Signal Strength setup screens, I individually choose which tuner is used for which stations. However, stations not detected by the first tuner (a Hauppauge 1250 connected to a UHF-only antenna) are not offered for the second tuner and must then be added manually. Those manually-added stations don't have guide data.
In the WMC signal strength dialogs for the 950, it shows no signal strength for even the strong local channels, but they are received and played perfectly in WMC when they are selected for the 950 and deselected for the 1250, so the 950 works fine, other than reporting no signal strength to WMC. I've been using the latest Hauppauge driver
for it, so I don't know what to try next.