Original vs. upgraded Mark Levinson 390s

I would like to buy a used 390s and have noticed that everyone wants an original unit, not the upgraded ones. Could someone tell me why? I am more concern about the sounds than cosmetics changes. Thanks.
I think you will find that the most common reason is the residual values. Easier to sell on. Also a lot of the upgrades do not have the 390s faceplate. A very expensive cosmetic change relatively speaking.
The upgrade does not change the transport. The new model has a different transport and is better. Otherwise the same. But thats enough to affect the sound !