Hum, we prefer real sound here, don't take it in a
bad mood !!
There might be samples that are better than FM synthesis, but I don't
know any free sample that is better. The DX7 sounds are very good. Since
it seems to be possible to load DX7 sounds to Hexter, IMO you should
test it. I guess there will be a lot of DX7 xylophone sounds available
by the Internet.
I know that Hexter's default sounds aren't good, but usually vibraphone
and xylophone sounds for the DX7 sound more natural than free samples
do.
Sample player sounds aren't real sounds either, if they don't use
layered samples for every key ;). I suspect you won't get such a super
sample for free, perhaps illegal by torrent :(.