Why Scott McKnight kissed Calvinism good-bye

Looking back over Scott McKnight’s always-interesting blog, I noticed this post about his dalliance with Calvinism (or, at least with some Calvinist writers) and why he couldn’t, in the end, accept Calvinism as a ‘system’, much as he admired many aspects of it.
He writes:-
I love the “architecture” of Calvinism — that is, the focus on God’s glory and loving God, and I love the magnitude of grace in that theology, and I even love the radical transcendence that is often found in Calvinism…
When I was in college I sat for afternoons in our library and pored through Calvin’s Institutes, leading my dear wife to comment that I’d be better off underlining what I didn’t like because I had underlined most everything! Calvin’s Institutes are doxological; I still dip into him and read him. And, at the same time, I was a huge, huge fan of Spurgeon and read his Autobiography twice while in college. And, of course, other Calvinists banged around my desk — like the ever-wordy John Owen and I read devotionally John Brown’s commentary on Hebrews and Manton on James.
Then I went to seminary at Trinity [Evangelical Divinity School], Grant Osborne asked me to be his TA, and one of his first assignments was to work through his extensive notes on the Calvinist-Arminian debate. Which I did. To be up to snuff on it, I read Howard Marshall’s Kept by the Power of God — and my mind changed. Not all at once, but this is what I remember: the consistency of the OT warnings for the covenant community formed a natural bridge for me to the NT warnings. And I couldn’t contest his many, many passages that all added up to one thing: genuine believers can lose their faith by throwing it away consciously.
Then I began teaching at TEDS, then I was asked to teach Hebrews, and then I made a special study of the warning passages in Hebrews, and from that time on I was simply convinced that no matter how much I liked the architecture of Calvinism, I couldn’t believe the system (TULIP, etc) because of the warning passages in Hebrews — and they then influenced how I read such things as Col 1:23 and the like. If the warning passages in Hebrews are what I think they are, then the systematics of Calvinism are unbiblical — lest, like one of my TEDS colleagues, you think both sorts are found in the Bible.
Now, where’s my copy of Marshall’s book, and what does an unrepentant Calvinist like me make of those warning passages in Hebrews…?