I had a similar question once and consulted with a friend who had a Krell KSA 50 (I think it was). He said the Krell instruction manual said specifically NOT to do it. If you have the instruction manual, take a look. I'm assuming you are talking only about the connections, not using them at the same time (obviously).
However, I asked this question to Hafler once (for a pro 9505 Transnova amp) and they said a concurrent connection wouldn't be a problem, presumably since the Hafler amp has a switch to go from XLR to RCA, so that either one or the other is engaged but not both simultaneously.