Change of level between taps. 1 watt at 8 0hms is 2.83 volts, 1 watt at 4 ohms is 2 volts. Which light bulb will be brighter, 2 volts or 2.83 volts. Which speaker will play louder, 2.83 volts. The voltage determines the level, not the load. If the load changes to a lower value the amp has to put out more current and the amp runs hotter. As long as the power supply is strong enough and the transistors can dissipate the heat and the quality of the Autoformer is adequate, there is no issue. But as is in your case where you like to push the envelope you should be using the 4 ohm tap. Now one thing a 501 will do is surpass specs if you attach a 4 ohm load to a 8 ohm tap, because of its high current reserve. But you as with your 252 you have to supply extra cooling to remove the heat generated from the power being produced. I don't know if you knew, but back in the 70's when the FTC changed how amps were to be rated, Crown had to supplement the existing heat sinks on the DC300 A with clip on heat sinks. Where 2105's 2505's and 2200 and 2120 didn't. Today with the Mac amps being able to supply extra current for todays complex speaker loads, the supplemental cooling is required if you don't follow the directions in the owners manual which states if the impedance drops below that of tap being used you must use the next lower tap. So because the speaker is 6 ohms you are to use the 4 ohm tap, even though the sound is just fine from the 8 ohm tap. If you choose the 8 ohm tap you need cooling because you are using a lot more current. Plus the louder you play your speakers and the longer you play your speakers the impedance of the speaker changes causing more strain on the amp. If you read JBL's manual your speakers are starting to suffer compression at any level above 10 db below the maximum rating of the speaker. So if your speakers is rated at 500 watts, any time you go above 50 watts the speaker output is dropping off and absorbing more current while decreasing in sonic output. I'm not saying your speakers are bad, all speakers compress. You just need speaker further up the chain for higher linear output levels. DD65000, maybe or 4435.
