We are all looking for better sound recordings, so you aren't alone!
In your case:
- I agree with Chris on the 888hz as being too high. Cards seldom need rolloff at all, omnis do. If you want some, try 80hz.
- Where you are in the crowd, and how you point your mics is probably the most important piece of the puzzle. Since you have cardioid (directional) mics, you can't just have them pointing random directions. They need to be pointed forward and preferable out at something like 90 degrees with respect to each other (45 off from front). This is where your stereo image comes from. IMO stealth tapes seldom have good stereo image anyway, because hidden mics are seldom optimum. Keep in mind that most shows now seem to have a pretty mono mix... same things coming out of both stacks, and there's nothing you can do to fix that.
- Recording at 96khz doesn't change the way it sounds much. A high bit rate just records whatever signal you get with higher resolution. It can't improve the signal.
- With mics > battery box > recorder, your recorder provides preamp and A/D converter. If you prefer the sound of your old D100 to the new D50, that's a legitimate preference, but that should be a relatively subtle difference.