Confused for the best connection between my Elac speakers to power Amp

Try both. If you can hear any improvement just leave it on the tap that sounds better. I doubt you will hear any difference!

Tried both no difference. I do not want to harm the output stage of amp or input stage of spkrs

Use the 4 ohm tap. Impedances will fluctuate. 

Use the 8 ohm taps, you will get the best out of the amp.   My speakers are rated at 6 ohms and the 8 ohm taps on my MC302 ampsound the best.  In my office system, my JBL speakers are rated at 4 ohms and also sound best on the 8 ohm taps on my MA6600 integrated. 

Thanks. will give it a try. Are you sure it doesn't overload (sink high current) from output stage of PowerAmp? 

No worries impedance is approximate. 4 or 8 will be fine. The only real worry is that you have something crazy like 1 ohm speakers and the amp can't manage that low of an impedance. You are fine. 

It is strange when I was a kid. 16 ohm speakers were real common, 24 ohm.. I still use the highest ohm out just for the tube breakup. Tube amps don't normally double in wattage they stay the same. 2 ohms to 24 ohms that Mac will put out about 75-80 WPC. I let my ears tell me the story. High E speakers, above 90% they can get noisy, that TAP can make a difference. Just listen..

Regards