What I've just got working is to run my guitar into my 18i20's instrument input, then out the back at line level into a radial JCR reamp box, into the amp. This works because the 18i20 can function as a mixer and directly connect (as far as I can tell) preamplified inputs to outputs. Maybe your...
I think I've avoided it out of principle, and stuck to the version with the original musicians before Sharon et al. tried to screw 'em over in that particular way.
There's the RickToone tremolo, which has an individual cam per string so everything stays in tune, but it looks like it's only available for volume licensing and not as an after-market parts purchase. I don't think it can do all the fancy stuff this one does, just the relative pitch preservation.