Newbie question - dedicated headphone amp or is my McIntosh MA352 sufficient

Not sure if your phones and amp are a good impedance match, the specs don't say. Try it first, the Mac headphone amp should be good enough. 

Headphone amps in integrateds are usually a bit of an afterthought, and McIntosh doesn’t specify the headphone power output of your amp in the specs, which would lead me to believe it’s nothing special — could be wrong though.  The HE1000s do require some power to get the most out of them, and frankly I think a $3000 pair of headphones deserves and will greatly reward you for a better headphone amp.  Just my $0.02 FWIW. 

agree with soix

I doubt it, but haven't owned your McIntosh. A good headphone amp is essential for getting the most from your headphones, and most included headphone amps are far from good. 

If you’ll be doing much headphone listening you’ll be happier with a dedicated amp. A good power supply is important, that’s what sets it apart from your built in headphone section. Audition with your headphones if possible.