I don't find that preachers work, either machine or barbell. I feel them in my elbows and front delts, and nothing in between. Like whitey said, I think it's to do with arm lever length.
I went from using a lying hamstring curl at my old gym for 3 years to using a seated at my new gym, and it felt horrible. I've played around with the adjustment settings and made it sort of ok, but it just doesn't feel right. You're contracting your hamstrings, yet you're sitting on them, getting squished into the seat. It's just a bad design.