The best thing I've found is to stay away from triads and do more 8va unisons and maybe a 5th harmony. Playing horns with a keyboard is always iffy. Real horns don't come on like a switch, there's more variation in velocity. The best way I've found to lay down horns is with a breath controller. I wasn't real crazy about the horns at the end. Drums don't have as much of a problem as even real snares and kicks (especially through a compressor) can sound very similar hit after hit. Our ears are always searching for patterns and in real drums it is virtually impossible to hit a cymbal several times in a row and for it to sound the same each time. What you end up with is that each crash sounds a little different and is in a slightly different pan position.
Play clusters of two or three cymbals together with the notes space slightly apart and each one is a different combo of velocities. What I've done before is: the snare, kick an hi hats are quantized but lay down the cymbals using a keyboard and don't quantize them. Usually the drummer will have a crash on the left and on the right. To me the drums didn't sound too bad at all (kick could use a little presence) but what was crappy was the crash cymbal being identical several times in a row.