I absolutely agree with you, it should be very possible to test out an H8000FW before you buy if you can find a place to test it out. I am sure Eventide will be able to help as bhaberman points out.
Meantime, in case you didnt see it there is a good audio demo on the H8000FW webpage created by a fellow user called Matthias Adloff a few years ago and will give you an idea of its capabilities. Here's the link
Also an audio demo by an ex Eventide staff member and programmer Italo De Angelis on the following website
but plenty of other tracks on his Eclipse page which will give you an idea.
Dont forget you can also create your own algorithms using the VSIG editor. This allows you to program new sounds or to edit existing presets, although it is quite complex and you'll probably have to invest some time to get to grips with that.
But here are some related links.
Hope that helps, and look forward to hearing your views when you have had a chance to try out the H8000FW in person.