Ask HN: How do you hire a senior programmer when you aren't one

I've inherited a cross functional team, and the lead programmer has moved on.

I'm an experienced dev, but not proficient in the stack for which we are hiring.

I'm in the process of replacing him.

There is a technical test in place which I am asking other developers to grade, however I have questions about the grading, and of course the test. We're passing or failing candidates based on the test, but I know the best person won't always be the best test performer. Further, someone could not 'pass' the test and possibly be good.

Does anybody have any magic to share here?