I never cared for biamping my M19's either. And I used identical amps for highs and lows. PP 6B4G modified Heath W5's. No sand amps in my system. The issue was probably my x-overs, but just never messed with the whole thing because the stock x-over just sounded better.
I have messed with 6db slope stuff. On A7's as well. But the woofer section has a peak at 250-300hz, and that just became accentuated. To my ears anyway.
So Jeff, do it and have fun and tell us what you hear.
Ron