I've got to chime in here about carbon.
Our tandem AL had a steel fork- DH hated it. Lots of vibrations.
We swapped in a carbon fork and he couldn't believe how much it changed.
I don't think you should discount carbon totally- the build and geometry of the bike does affect vibration as well.
Thgere's other things that can help vibration- gloves, gel bar tape, carbon handlebars, having flatter tops and the shape. Also riding position (being more upright so less weight on the hands).
I guess it's a case ot try, try try and don't discount something because it might just work for you.

