I agree with Melissa, the water ratio maybe too high. Dental die stone won't crumble unless the mixing ratio is way off, mixing procedure is not correct, or the stone is not being properly stored. I would also check how long the stone sets.When I did models long ago I poured them the night before and in the morning I would have great detail and strong first pours to work with.
The only way I know to accurately finish an emax inlay is to:
1) Wax up inlay over a lubricated die with die spacer, make a sharpened sprue connected to the inside of your wax up
2) Invest with a ratio allowing for a slightly looser fit than your crowns
3) Carefully devest and fit using a fit marker
4) Adjust margins with a silicone, fit, adjust contacts, smoothen with silicone
5) Glaze and stain
I would say broaden your horizon. Emax offers so many ingot types that its too hard to say in general. But I can say that HT ingots are good for posterior stain technique, but if the wax up is too thick, it will be too gray. You can also use Value ingots in these situations. LT ingots are good for copings, but I find value ingots to work slightly better if you have good build up control. Hope this helps.
Though I love the idea of lab management periodicals I would always suggest learning from the business perspective and applying what you learn into what you know in dentistry. I also see a benefit in learning IT management with the growing CAD/CAM equipment. As a graduate of business I can say that if you know the ins-and-outs of how a business works you can apply your lab experience to make sound decisions. Good Luck!