If you have a desktop computer with a separate 1080p monitor that has a HDMI input, and an antenna/CATV connection is nearby, then using your computer monitor is an option to a HDTV for displaying the output of the 3500STB. I am borrowing my 23" monitor from my desktop computer, with a HDMI cable between the 3500STB and the monitor.
On a separate issue, I use CATV, as few OTA stations are available where I live. But since I could build DIY 4-bay bow tie antenna quite inexpensively (see several YouTube videos on how to build), in the spirit of playing around, I am planning to see what OTA channels I can get. Do I assume correctly that I can set up for AIR rather than CABLE, then do a manual scan to add any OTA channels? I plan first to connect the DIY antenna to my HDTV, do a scan for OTA noting the frequency for each channel, so I will know what to expect from the 3500STB. I have gone through a lot of work to scan and label 93 clearQAM channels of 103 available clearQAM channels, and I wouldn't want to lose that on the 3500STB. I have labeled only the HD channels on my HDTV, so potentially less work to lose.
Please correct me if I am wrong about adding OTA channels to my scanned clearQAM channels.
Yes, that is how to do it - a manual scan. Be careful not to hit the auto scan, which is easy to do accidentally, or it will erase all your channels.