I'm still wondering why your slabs have cracked/split. I wouldn't mind knowing what the problem is and how to fix it.
Another contact option is to do a search for Slab Furniture or Live Edge Furniture, to find makers of this type of furniture.... there are quite a few. Not sure if they will advise you, but it wouldn't hurt to try getting related problem-info from them. I would suspect they have had similar issues.
I've made ER cedar slab tables, but have never used epoxy, nor have I tried filling gaps. I haven't had any gap problems or expansion/contraction problems.....yet! The slabs I've cut seem to remain solid, not check, so for. Example: Book-matched ER cedar slabs - http://www.flickr.com/photos/43836144@N04/7327627522/
I've cut cypress and live oak slabs and those slabs checked badly, so I've never made any slab tables with those. I think those checking problems were drying related, not exansion/contraction related, specifically.