There is a reason I don't need to google some things, and that's because I have personal experience of the same.There is no underscan issue with my 690G or 780G on either my 3008WFP or my Philips LCD TV. I get 1:1 pixel mapping to my Philips LCD using the scan controls. Yes some adjustment is required (only when connecting to the TV) but after setting it to 10% overscan I get a pixel-perfect picture.
As for LPCM over HDMI, anybody who is setting up an HTPC of some mettle will need a proper audio interface anyway, as onboard outputs suck for any kind of audio use, through either digital or analog outputs. Since you are such an experienced person, you would already know that, wouldn't you? I of course assume you are using LPCM over HDMI out of the box, do compare it with the SQ of a dedicated sound card (even using a digital output, the difference is pretty startling).
I see you're pretty worked up about this whole thing. Without undermining your experience or your advice, Google is just a helpful tool. Checking back on your doctor by using google is not advisable, safe nor recommended. Please be careful when handing out dangerous advice, as these kind of things can kill people. I would suggest sticking to audio, electronics and PCs, as a starting point. And even there, Google is not the end of the world. They change their algorithm every 6 months, and even then they get it wrong sometimes. So don't place too much faith in what Google tells you. Try it yourself. I'm not about to bandy my years of experience and all the things I have done, as that is poor etiquette and in generally in bad taste. Suffice it to say that it does not entitle me to expect people to take my word for things I say, and neither should you or anybody else.
And like I will continue to say, do not assume your advice is 'right' and immediately everybody else is 'wrong'. There is no point in having a discussion forum if there can be no discussion, and if people start insisting on using words like 'right advice'. Such a thing does not exist, for your experience and others' can be very different, such is human life. Of course, since you seem to find such a thing offensive, I see no reason to continue this discussion.
Have a nice day.