I did that for a while...worked fine for me.
You are correct. You do not need HT pass-through. You can use any unused input and simply calibrate the HT setup using a pre-defined position of the volume control on your pre-amp. When I've done this in the past, I used Top-dead center of the volumen control as the point where I calibrated the HT setup and sat the volume dial each time I played HT though the system.
Admittedly, HT pass-through, especially if controlled via the remote, is a nice feature. But it it completey unnecessary. It's just a nice convenience.
That's why you don't use MAX volume as your reference point. I've thought about that issue and the answer might be to use "loud" on the volume dial as the reference point instead of something like top-deal-center. You might want to choose one of the other sources, determine what volume level is "loud" and use that level as the reference point.