I can tell you 1" is asking for trouble as I own one. My rack is open on all sides and I used to have about 2 to 3 inches clearance above the amp and it still occasionally went into shut down mode about 3 times in a year.
I have now removed the component on the upper shelf that was previously sitting above the Luxman. Everything is good now and the amp works flawlessly without shutting down by itself. By the way, the L-590AXII is a great sounding Class A amp, a very high quality integrated at its price point which is capable of stellar sound quality when properly optimized with equally high quality speakers, ancillary equipment, accessories and cabling.
Enjoy ~
I have now removed the component on the upper shelf that was previously sitting above the Luxman. Everything is good now and the amp works flawlessly without shutting down by itself. By the way, the L-590AXII is a great sounding Class A amp, a very high quality integrated at its price point which is capable of stellar sound quality when properly optimized with equally high quality speakers, ancillary equipment, accessories and cabling.
Enjoy ~