Ergo 122 question

[Ghost rider]

I recently bought a Rogue ST100 tube power amp to run these and on the amp I have a 4 or 8 ohm loading option and on the speaker it says 4/8 ohms. When I demoed the amp I thought it sounded a little better using the 4 ohm binding posts, so that's how I left it.

I have wondered is that correct, is the speaker 4 ohm under normal use and 8 ohm if by-amped? My understanding if you connect 2 8 ohm speakers parallel you create a 4 ohm load and that makes since as to why and how I should connect them to the amp.

Also I have had these for almost 20 years and at the time I got the shielded option because of a tube TV concern a 35inch set. How does shielding change the sound?