Balance in Nature/Double Advents/Impedance/NAD2600

New to my domain is an NAD 2600PE amp that I'm using with a pair of 8 ohm Advents per channel wired in parallel, which should present a 4 ohm load at the NAD's output.

The NAD has an impedance selector. The 4 ohm position is labeled "NORMAL" and the 8 ohm position, "HIGH".

There's also a message on the back of the amp which cautions to use the 4 ohm position only when the amp is in bridged mode, which is not how I use it.

Maybe I had better wire the speakers in series (giving 16 ohms) and select the 8 ohm impedance setting?

Or am I safe as it is?

And the NAD has on its front panel input level controls for each channel. Where are these best set? Is it a matter of trying various positions to find the optimum or are they best set at max?

My interest is not to swamp my ears and upset the balance of nature with sound, but to have smooth, sweet, listenable music...

I welcome your advice and comments.
The amp should be fine, If the amp were bridged into a four ohm load it would see a two ohm load. You would not want to run four ohm speakers with it in bridged mode. The level controls should be set a max unless you need to adjust in a bi-amp setup.
Set your input level controls on the amp to max and your impedance switch to 4 ohms. If these are the older (original Henry Kloss) Advents, they dip a little below four ohms. The NAD should be fine with this.
I ran one set at 8 ohms into a 4 ohm impedance some years back and had no trouble. It sounded better that way (more powerful)
Also, I believe this amp has a soft clipping control. If it does, turn it off. You don't need it.
Advice taken. Thanks very much. Now let's advise the US Government on a few issues like power handling...