Resolved: it was not a code compatibilty issue at all. It turns out there was a broken wire on one of the IR emitter leads. The wire is very thin and the insulation is is pretty soft, and it must've gotten nicked at some point along the way. They're probably wired in series, which would explain why a broken wire on one lead knocked out both emitters.
btw, I was able to troubleshoot this by doing the "digital camera test" as suggested by Sling tech support. Too bad I had to pay $29.95 for the suggestion, but all's well that ends well.