If you don't have a standalone RTA setup, get an RTA app for your phone and see where you are.
Are you using the M15 xover? No filter on the woofer in the M15, I think, so the woof impedance doesn't really matter, but the 902 should be 8 ohms.
I think the M15 xover has a MF notch and an HF control which changes the peaking network but it is not a volume pad, per se.
Properly balanced, that bent horn will be a bit on the smooth and laid back side, which is a good thing about it. It is definitely not an in-yo-face sort of horn.
PS: Hey Walt, you can't get a Western Electric horn system for $50k. Try several times that figure! 5-10X that figure for the good stuff on the Asian luxury market.
Deja Vu is selling GIP replicas. You can get a decent entry level GIP system for $50k. Talk to me, I write their brochures and I can get you a good price!
I'll try to get my GIP 18"ers running for the next Capitol Audiofest. They are pretty good speakers.