[Sonic Defender]

@mikebarber excellent points to consider for sure. In my case I seem to have zero issues at all, including turning the amp off with the headphones connected (I don't hear any thump at all). As well, I have no noise that I can detect with my headphones, but neither are sensitive so I can't assume this would hold true for more sensitive headphones. I'm lucky in that the M3 is quite well designed in terms of clean, stable power regulation, and for certain not all amps will be ideal candidates for a speaker tap. So for certain, know the headphones and the amp before deciding what to do. I e-mailed NAD technical support to make sure of the ground situation (in my case it was a common ground) so I had a nice balanced cable made.
 
I have had zero issues whatsoever using a moderately powerful amp (180watts at 8ohms), but it is very good that you took the time to caution people as you did.

 

[Sonic Defender]

There is a very good auction happening on e-bay for a used NAD M3 and it may go for a very good price. It is an excellent amplifier and very well reviewed. If it sells for anywhere near $500 it is a complete steal. You get a great speaker amp and an amp that can be used for headphones via speaker taps. If anybody is looking this is an excellent candidate to consider.
 
http://www.ebay.com/itm/NAD-M3-Dual-Mono-Integrated-Amplifier-2-channel/141588534333?_trksid=p2047675.c100011.m1850&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D20140602152332%26meid%3Df66a168b8c6c475ca2d1c68b70ecc0ee%26pid%3D100011%26rk%3D1%26rkt%3D10%26mehot%3Dpp%26sd%3D131273100858

 

[nicholars]

  There is a very good auction happening on e-bay for a used NAD M3 and it may go for a very good price. It is an excellent amplifier and very well reviewed. If it sells for anywhere near $500 it is a complete steal. You get a great speaker amp and an amp that can be used for headphones via speaker taps. If anybody is looking this is an excellent candidate to consider.
 
http://www.ebay.com/itm/NAD-M3-Dual-Mono-Integrated-Amplifier-2-channel/141588534333?_trksid=p2047675.c100011.m1850&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D20140602152332%26meid%3Df66a168b8c6c475ca2d1c68b70ecc0ee%26pid%3D100011%26rk%3D1%26rkt%3D10%26mehot%3Dpp%26sd%3D131273100858

 
Just SLIGHTLY overpowered for headphones LOL 180w RMS with 785w Peak

 

[Sonic Defender]

   
Just SLIGHTLY overpowered for headphones LOL 180w RMS with 785w Peak

That is what I run my headphones with, and not an issue at all. Simply love the combination. So far my 560 and the ZMF Vibro are fine.

 

[nicholars]

 
That is what I run my headphones with, and not an issue at all. Simply love the combination. So far my 560 and the ZMF Vibro are fine.

 
Just make sure you do not leave the volume knob up when switching between speakers and headphones!

 

[Sonic Defender]

   
Just make sure you do not leave the volume knob up when switching between speakers and headphones!

No issue, my speaker tap cable is on the previously un-used speaker B circuit which I must deliberately switch to for headphone use not to mention, I am always careful with where a volume pot is left at, this is important with speakers as well so a good habit regardless.