Time Aligned Boards-Who needs them??

The time aligned boards tend to offer a tighter more rhythmically adept and more forward sound, whereas by comparison the 324s are a bit softer and a bit more diffuse.

As with all of these old shoeboxes, the sound can vary due to age and batch. You may have a really good set of 324's and a sick and tired set of 729's.. Only way to really hear the difference is to have both sets of boards serviced and then do a shoot-out. I preferred the 729's , you may like the 324's. 

Comparing a 72 to a 52 is stretching it a bit, no  ?

So is a 72 with 324s replacing the 729s identical to a 32.5?

No. Quite apart from age and variants (even among the earlier NAC32.5s - "artwork" boards etc.. and NAC72s), a NAC32.5 offers a Mono switch, which is omitted on the NAC72.

I mean sonically... Are there any noteworthy differences?

Sorry Richard, I am not clear on your last post.

Mikeybaby, even when new, while both the NAC32.5 and NAC72 were superb pre-amps (and indeed, still are) there was a degree of variance from one sample to the next (things are a lot tighter these days).  Age and use have just widened the variables, so any answer here is of little use; you have to take any example on its individual merits.  They will all be cut from a similar cloth, as it were, but there are some very special examples and some that are, well, not so special.  But what's special to me, may not be to you, and vice versa.  For example, one of my NAC32.5s sounds very smooth and a bit soft up top - this despite a service not that long ago. For me, it lacks the excitement and immediacy that I know is possible with a rather special example that I still have.  But for you, it may be lovely and my "special" example may be too forward, pushy and not diffuse enough for you.  Do you see the problem?

So, if you want the best shoebox pre-amp for you then the bottom line is this: Listen to as many as you can.  If you can't do that easily then just go buy one, go buy another, buy a bunch, and then keep the one you like the sound of the most, but whatever happens you will have to listen...

I see ... thank you.

Upon full warm up it seems the 324s are missing a bit of that 729 sparkle...

With circuits 729, excel energy, better control distribution audio frequencies. Very good !