Is EQ'd playback on Mac into Naim bit perfect?

IIRC, a Mac using iTunes is bit-perfect.

However, if you include the likes of Fidelia or Amarra etc in the mix, then I'm not certain 

If it's EQd you've played with the original signal, so it isn't bit perfect, no.

Am I right in assuming that iTunes on a PC is not bit perfect? Because there is no way to select WASAPI or ASIO or Kernal Streaming as far as I can see... ru.. *cough* ..bbish.

Nope you can't, and yes it is.  If you must use iTunes on a PC then you can use the multi-plugin to alow iTunes to fob off the processing to fubar (and do the wasapi thing).  That way you can use iTunes organisation, tagging, syncing but not audio processing.  

Like John say's it's not bit perfect, only unaltered signal will be.

What matters most is your musical enjoyment, i use EQ and couldn't be without it.

Bit perfect simply means the data is completely unchanged compared to the source. EQ alters it, just as windows re-sampling does. 

Ignoring the 'bit perfect' part, whether or not EQ degrades the sound depends on your definition of 'degrade'.  It degrades it in so far as what you're listening to is not an analogous representation of the original audio file, because you've adjusted the tonal balance.  But if that makes a particular track/type of music more enjoyable for you, then it's hard to argue that the sound has been degraded.  Same thing goes for any tone controls, including the once-ubiquitous Loudness button.