With virtually all solid-state amplifiers, there is no chance of damage if you run them without speakers connected. The output circuit is designed so that no current flows and nothing oscillates if there is no speaker load. Even so, with A/V receivers, I recommend that you go into the menu system and "tell" the unit which speakers are connected and which are not so you hear all channels from whatever speakers you have.
Tube amps are a different story. According to Mark Peterson, HT's audio tech editor, "In most vacuum-tube output stages, there is a tuned circuit utilizing a transformer with the primary connected to the output tubes and the secondary expecting a speaker load. If the load is missing, the circuit becomes de-tuned, so oscillation is likely and the output transformer gets hot (at the very least). Fender tube-based guitar amps (and probably others) have internal resistors that switch into the circuit when the speaker jack is empty to protect the output stage, but hi-fi gear rarely has such protection."
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