The tech is right. That HDMI cable at 25" is far too long for current practice. For that length you need a hybrid optical/copper active HDMI cable. You will also need a
voltage inserter so you don't blow the HDMI ports.
I recommend Ruipro, which is what I use, as I have a long run as well. A 10 meter cable is what you need.
Make sure you install the cable the correct way round. They are directional. The converter with the arrow pointing away from the end goes at the receiver end. The arrow pointing to the device goes at the TV. Then the correct converters are at the correct locations.
You absolutely should have your receiver wired to the Internet. Not doing so risks crashing your receiver, and having to send in to have the BIOS re-flashed.
You don't want tight wires in that conduit, so you need to bite the bullet and open up walls as you need to, to get this right. As always, engineering has to be right, and at its foundation is correct and robust installation.