To amplify (no pun intended, heh, heh) JohnK's comments, gradually increase the volume as you check the heat radiated by the receiver. It should get no more than warm to the touch. If it gets hot after driving your 4-ohm speakers for an hour or so, I'd say you're likely risking either blowing the output stage or thermal shut-down.
Protection circuits of various types have been around a long time. An early solid-state amp I built in the late '60s (a kit) had thermal sensors on its output transistors to shut down the receiver if it got too hot. Without seeing the impedance curve of the speakers, it's hard to know whether the curve just touches 4 ohms at one frequency or remains there over a good part of the spectrum. If it were the former case, the JVC might drive them with no difficulty.
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