Black on black, or is it a grey area.

It's probably down to the fact that the entry level kit uses a slightly textured powder coat finish.  There can be some minor variance depending upon the batch depending on the light and angle. The difference shouldn't be huge, although I guess at one extreme you'll have a texture that is smoother and at the other extreme a heavier texture which can lighten the black.  Back when I was at the factory, Naim's QA dept. had examples of the allowable extremes and any of the painted Magnesium Zinc parts that exceed these extremes were rejected.  I would guess that still applies.

Cheers Richard, Both have the facia's of the current XS range. The differences are in the anodised areas and not that great but can be seen in certain light and angle.

The 172 simply look shiner, maybe that's just the nature/freshness of the unit, and the 155 being a poweramp produces heat so has a slightly dryer/warmer look?

Or will the difference/shiner/wetter look of the 172 tone down in time?

Ah Ok, sorry, just realised that your kit has anodised 5 series fascias not the powder coated zinc alloy casting.

With anodising is almost impossible to keep things absolutely identical over so many units and years.  The trick is to keep it within a limited range of variance and ensure that problems such as roseing or flatting don't occur over time.  It's quite possible you might see some very slight difference in certain light.  Only way to pretty much guarantee a perfect match is to get they fascias from the same batch.  And even then...

As per the powder coated finish, Naim's R&D keep the anodised fascias within a reference range of possible and allowable variance.  Any just outside of that may go to seconds for staff build or if obvious, to the reject pile.

As you can see, not obvious

Will a bit of wax as shown above work and is it recommended?

No that was a joke...don't take anything I say seriously...except this:  Throw away that "High School Musical 2" DVD.

I have NDX & Supernait that both have the anodised finish, they are aprx 5 years apart in mnft age.  Their is a small variation in finish if you look closely,  the surface texture & light reflection are different.  I've assumed it was a change in the bare metal surface prep and/or could be a different anodising plant. I also have a NAT-05 that has the powder paint finish & that is a lot different.  But we are talking close visual inspection & also touch w.r.t. anodised -v- powder paint.   In day to day use & at 1m away its not visible  ...  & no they do not appear to be changing (toning down) & TBH I would not expect it to. 

Secret message to your OCD self (other self do NOT read): 

Did you know you could just trade them in, and buy new ones with EXACTLY matching coatings?

Wheres the fun in that, couldn't wind my OCD self up then...

Spacey - I'd be more worried about the angle it's at. 

OK spacey,  I have OCD with 'lecky stuff me-self

The cab is my own design & build.  The stuff with buttons is all visible as shown,  the PSU's, phono amp & the 8 way power strip with DC filters live in a lower section with a door.      

Tiz an old house built by Geordie reivers over 100 years ago, its quite normal in them there Northumbrian hills

Nice work.