First and foremost, you've already tried the top manufacturers arranger keyboards, which is good. What you failed to do was test them using headphones, which is very important. Headphones eliminate using the keyboard's onboard speakers, which very often are custom tuned to get the best sound out of the keyboard.

I believe the problem is not the keyboards you used, but instead the church sound system. Most church sound systems, while very expensive, are not particularly good for reproducing high-quality music produced by electronic musical devices. The systems are primarily for vocal reproduction, and most of the systems I worked with many years ago were EQ'd to Flat.

My best advice is to first check out the church sound system and try to tune it to sound as close to your keyboard speakers as possible. Most are multi-channel, and you may be able to assign a couple channels for just the music, while the others are still in the flat mode for sermons and choirs.

Good Luck,

Gary