Rob I think Athena ones are good quality with a thin rubber coating just like yamaha ones, perhaps you can confirm this. If so you wouldnt 'need' to use sealant, however personally I think a thin 7mm wide wipe of silicone manifold sealant around the circumference of the bore (each side of the gasket) is good practice, I read an awful lot of DTR head gasket reports. If you are using a cheap pattern all metal gasket then the silicone is a must...whatever you do though dont cover the whole thing in it as you will struggle removing the head at a later date.