4 8 or 16 ohms.

Look at the impedance graph in the speaker review. It's all over the map.

The amp will sound different on each tap. Choose the one you like best. It won't hurt the amp or speakers.

@larryi Transformers transfer maximum power when source and load impedances are equal.

The people advising you to use the tap that sounds best to you are correct(Don't waste your time with 16 ohms). And there's np danger with any tap as advised. As to power with your amps there will be way more than enough power with both the 4 and 8 ohm taps.

It does matter. I had an amp with two sets of red binding posts. The manual made no mention of the purpose so I connected black to black and red to the post nearest to black. Long afterwards someone suggested one may be 4 Ohms and the other8. Via Audiogon I verified that and I had been connected to the wrong impedance. The sound when I corrected my mistake was clearly better. It matters.

Always use the recommendations of complete strangers over your own hearing as hey, you don't want to insult anybody.

Thank you everyone for this explanation of ohms. I’ve been putting together sound systems since I was a teen but never bothered or had the need to understand this until now. One of my friends just gave me another example of this. I think it was a good one too so I will write what he wrote. Short answer try 4 and 8 ohms. The difference between 4 8 and 16 is how much electrical energy there is to drive all the speakers. 4 ohms is a heavier load than 16 ohms.  A 4 ohm speaker will extract more power from your amplifier than an 8 ohm speaker , about twice as much. Think of pushing a heavy ball up a hill. The load. The woofers take the heaviest load and take the most power to move. Most box speakers like B&W are 8 ohms settings overall but dip to 4 ohms. Other types of speakers like 16 ohms. That’s why the amp has different settings. If u connect just the two 800 bottom woofers it needs 8 ohms. But if u connect the top two woofers also it is twice the load so 4 ohms is needed. The bass should be strongest with 4 ohms. But u should also try 8 ohms. With 8 ohms the highs might sound clearer u will hear more detail but the bass will be leaner. If u put it on 16 ohms it will really sound lean. It’s all subjective to the music u like and what u prefer. So try 4 and 8 ohms. You need to understand with a tube amp it works harder with 4 ohms. The tubes will have the least life in hours. It is opposite to the Krell FPB 600 u had. With the Krell design 4 ohms is easier. But it still sucks a lot of power and 16 ohms is harder on a Krell amp. Just different designs. Your speakers actually dip to 2 ohms at some frequencies. The Krell was made for the 800s and provides a very punchy bass. It will be interesting to see how the ARC amp compares. It’s not about how much wattage but the quality of watts. You can drive the 800s with a 100 - 200 watt amp. Hope this helps.