When you add the satellite speakers, you are decreasing the impedance (load) the amp sees because the load is wired in parallel, which actually means the amp develops more power. I think Herb is correct, particularly about the fixed impedance of one speaker, but here we are talking about two or more as the load for an amp: leave the satellite speakers unplugged.

A long time ago, I attempted to use my Peavey PA head as just a mixer. I thought it would be wise to place some resistors in place of the missing unpowered speakers. Knowing the amp was capable of 400 watts into 4 ohms, I thought I would be safe and used large 100-watt 2-inch long resistors on each channel. I did not even turn up the volume, but within seconds, the resistors were melting. Powered down real fast!

I concur with Rharv that unless the monitors were designed to be near-fields, they might work better at more distance (but still at ear level).

I concur with Scott about mixing at low levels, and I've said that here many times. There's a lot less ear fatigue over a long session. I always check a mix by turning the mix volume to barely audible, and if I can hear all the parts, I know it will work when turned up.

BIAB 2024 Win Audiophile. Software: Studio One 6.5 Pro, Swam horns, Acoustica-7, Notion 6; Win 11 Home. Hardware: Intel i9, 32 Gb; Roland Integra-7, Presonus Studio 192, Presonus Faderport 8, Royer 121, Adam Sub8 & Neumann 120 monitors