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No offense, but if you start doing whiskey/mashing again I'd strongly suggest finding a different enzyme supplier. A good supplier should supply you with the graphs and efficiency charts so that you can see where they are most effective, and where they actually begin to denature. Most enzymes have a point where they temporaraly denature and permanantly denature. Meaning if they just start to denature at 180, but are 100% efficient (at the right pH) you'll likely be just fine mashing at 180. Also by the time the pH crashes, your alpha should be 100% done doing it's job and it's time for the slower gluc enzymes to start waking up. I think my second enzymes don't hit peak efficiency til around pH 4.2 which is perfect for once the fermentation is rolling along. If your enzyme supplier just states "150 degrees" I'd look elsewhere because enzymes may be (relatively) cheap, they are the backbone of your mashing operations.

Lauter first and ferment off the grain. With proper sparging you should be able to achieve good yield

Try adding rice hulls to your mash. http://www.midwestsupplies.com/rice-hulls.html

Most of the rest of the world makes "single malt" by separating the grain before fermentation, almost exactly as beer brewers do. Use a lauter screen, don't add all your water at start , rinse remaining sugars (sparge) with rest of water. As mentioned above you could do several small batches. When/if you separate grain after fermentation I assume you don't rinse the alcohol out of the grain? You are throwing out some of your alcohol, but have happy pigs. A lauter screen works by the grain forming a fine filter bed on top of the screen. A screen could have slots of say 0.2 mm but if the grain bed settles properly it could filter particles down to 0.002 mm. During active fermentation most of the fines would drop through the screen. To trap those fines you would need to recirculate to the top of the grain bed. I very much doubt you could set up the grain bed as a good filter as I suspect the barley chunks would now be too soft and the bed would collapse and block. I would be very interested to hear if anyone has set up a decent filter bed post fermentation.