vandersteen 5 to 5a

My understanding is that Vandersteen originally planned to offer the upgrade as a field kit, but found that the process was too difficult to do in the field.

Apparently some of the replacement drivers have different mounting geometry, so new mounting holes must be precision-drilled in the head, and the old holes must be filled and sealed. The consequences of mis-drilling the holes would be catastrophic (ruined head), so apparently Vandersteen decided to make the upgrade factory-only.

As to whether it's worth the money - only you can decide that. I made my purchase after the 5A had been introduced. I auditioned the 5 back-to-back with the 5A, and chose the 5A. The 5 is a great speaker, the 5A is substantially improved. Quite substantially improved.

I do suggest that if you don't already have pretty much the best-of-the-best in electronics, the upgrade probably won't be worth it to you. If you do have great electronics, it probably will be worth it to you.

There were a couple of versions of the Model 5 - it has changed over its life. The variation in price on the upgrade is due to the change in price of the Model 5 - when it first came out it was around $9500/pr, IIRC. Part of the cost of the upgrade is some physical modification work that must be done to the Model 5. The older the speaker the cheaper it was to purchase, and the more work needs to be done to it to bring it up to Model 5A specs. Thus the additional cost.

That's the way it was explained to me, anyway.