Audio Research D75 to Infinity Kappa 9 high pass - which ohm terminals?

I don't post much but I lurk most days and have learned so much from all of you.

Today I received my Audio Research D75 back from repair after many many months. I was about to plug it back into the system and realized I can't recall which ohm terminals I was using on the amp. The shop was testing/playing it with 8 ohm terminals so I don't know if they had moved them.

Ultimately, my question for the experts is this:

If I am running only the high pass of the Kappa 9s, do I use the 4 ohm or the 8 ohm terminals on the D75? Kappa 9 official specs are 4-6ohms.

If the answer is 4 ohm, there is a very big message near the terminals that reads:

"CAUTION! 4 OHM TAPS ARE GROUNDED. AVOID SWITCHING SYSTEMS AND TESTING SYSTEMS WITH COMMON GROUNDS"

I use a Panamax MR400 Surge protector plugged into the nearest outlet, which is also a GFI outlet.

I'm terrified of damaging anything, especially after having waited for over 9 months (long story). So I can wait a little longer to make sure I get it right.

Side note for those who are interested or care, I've been running the speakers with a Peachtree GaN400 and it has not skipped a beat. I have an Emotiva XPA Gen3 I borrowed from my theater system before the Peachtree arrived and it was comically overmatched. The Peachtree will be employed solely for low pass in this setup going forward.

Advice and criticism is appreciated and welcomed - I learn from all of it.

Best,

Richard