Some of the measured differences will be less than a 1 db as you move up in complexity of Audessy. If you think you can hear less than 1db in measured differences, go right ahead and believe in the placebo affect. Your choice.
Given that 1dB differences are well within JND's at an awful lot of the frequency spectrum (depending on how wide the differences are, too), I would say that anyone who
doesn't think her/his ears can resolve such differences shouldn't bother with expensive audio kit...
I'm of the old school that an or a receiver's most important feature is its power supply and amplifier capabilities.
Based on the accumulated weight of listening tests, the old school view is simply incorrect.
If they can't drive the load loudly enough for a given room, then all the room correction in the world won't help you make it sound good as teh receiver begins to destroy the speakers.
While that's true, the fact of the matter is even cheap AVR's these days have a solid 50W+ per channel. Yes, some people with very hard-to-drive speakers may need more power, or a stiffer PS. But most will not.
Actually, if you are to swap out a pre-amp, with a new one, you'll have the old pre-amp sitting doing nothing unless you puchase another amp to use that pre-amp.
Think about it like a rational human being, and not an audiophool.
First, we're talking about receivers, not preamps. But let's leave that aside for a moment and assume
arguendo we're talking about preamps even though clearly this thread is about a new NAD
receiver and any person with the observational skills to notice a thread subject would know that.
If you swap out a preamp, you have an old one to either use,
or sell. So the cost of a new "upgrade module" is thought of by an intelligent person as
the cost of the module plus the resale value of your old piece.
Never mind that upgrading is a hassle, because one
loses use of the piece while it's being upgraded. By contrast, a parts swap does not suffer from the downtime problem.
Which is all to point out that the NAD modular model is just a bad deal on every level. A silly sales gimmick that really offers no benefit to the end user.