Ok, another update. I contacted SiliconDust and it turns out, in addition to the hdhomerun_config and hdhomerun_config_gui utilities/scripts/programs, the device has it’s own webpage. Just put in the HDHR device IP address in a browser and go (I bought my tuner used on eBay and have no documentation for it 
). From there, you can set your transcode mode (i tried none, heavy and mobile). However, once i started playing with this, the TVheadend server and/or the PVR addon in OSMC started acting funny (paused/skipped/dropped the stream and the PVR addon kept disconnecting from the TVheadend server). Just plain unstable. But… i reverted back to default settings for video display, the ones mentioned in @HarryL 's post above (post 3). Once i reset those settings to default, the video displayed in the correct aspect ratio (though was still not great resolution and the intermittent pausing stream remained). However, i did not rescan the muxes, yet 
Still desperate, i installed the HDHomeRun Live TV addon for kodi (URL that @HarryL listed above, post 6). It was super easy, with a caveat: I’m pretty sure you need the libhdhomerun-dev package installed. I already have this installed from my TVheadend endeavor. For info on installing that package, see @HarryL 's instructions on this, found in topic 1608 post 14 ( OSMC RC Unable to install TVHEADEND - #14 by HarryL ). If you follow those instructions, you will need to replace the following line (in the rc.local edit instructions)
/usr/src/tvheadend/build.linux/tvheadend -u osmc -g video -C &
with
/usr/src/tvheadend/build.linux/tvheadend -f -u osmc -g video -C &
With the HDHomeRun Live TV addon, you can force the transcode mode from OSMC. I used ‘none’ and have a great looking image with the correct aspect ratio and no stream disruption. The interface is not as intuitive (the channel up/down buttons don’t work… you have to use the right button to expose the channels, then the up/down buttons to scroll). However, you do get the channel name, like WHDLA or WSERE, etc., without the pain of setting up the EPG data. And, if you are using an antenna (in the US at least), the guide will be auto populated for you (my guide is not in the public domain, so the addon cannot fetch it… same issue on my Win7 WMC setup)
With all this said, shy of my problem being resolved once i rescan the muxes in TVheadend, it seems that there are some issues with TVheadend and the PVR addon. I know a bunch of other people are using this setup successfully, and @kphammond9 even has the HDHR (EXTEND??) device (same as mine) in the US up and running with this setup, although using an antenna (ATSC) not a cable (ClearQAM) input like i am. Using an antenna affords the ability to use predefined muxes, which doesn’t work for me. Again, a lot of people are defining muxes themselves, like i am, but not in the US with US-cable-irc type muxes, that i know of. If that’s you, please respond and let me know what you did… cause i’m pulling my hair out over this.