The only process is to 'try and see'.
I once had 6 ohm, 88db speaker with an impedance dip down to 3 ohms. Naturally I kept the amp on UL mode because that sounded better on most music and hooked the speakers up to the 4 ohm taps.
It sounded great! Listened to it for more than a year like this before trying the 8 ohm taps for kicks.
Well, the mid and upper band frequencies had more 'air'...and no discernable change in bass response.
Who would have thought. I wasted a year listening to the 4 ohm taps.