Re: E string constantly breaking
Are you breaking the same E string each time, of the two strings in the 1st course? Or is it sometimes the "outside" and sometimes the "inside" string?
If it's the same string, and if it's breaking at the loop each time, chances are that something's cutting into the loop, which would suggest the tailpiece post. You say you don't have to bend the string loop to force it over the "head" of the post, so it's probably not that you're weakening the string by flexing it at the loop. If you had one of the hook-style tailpieces, I'd be almost sure that a sharp-edged hook was the culprit, because the hooks are just stamped out of the metal of the tailpiece, and often have sharp edges. With a post-style tailpiece, a burr or edge on the post seems less likely, but the pattern of your breakage suggests this is the solution.
If there's no defect in the tailpiece post, you may have bought a couple sets of bad strings. The twisted loop is a weak point on strings, since there's a lot of direct-pull force on the "bottom" of the loop. I'd contact D'Addario and tell them of the problem you're having -- or else go back to the shop where they were purchased and see if they'll give you some single strings to make up for the one's that broke when you were putting them on.
Strings breaking at the loop don't suggest a rough bridge saddle, a too-tight, binding nut slot, or a sharp edge on the tuning peg. All those are legit possibilities, but the string's more likely to break at the point where the problem is. Yours aren't breaking at the tuning peg, nut, or bridge, so I'd focus on (a) the tailpiece, or (b) the possibility of defective strings.
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