I think most of us realize selling a collection as a "whole" is a great way to get pennies on the dollar, or less, for it. Going the DiscOgs route and listing individually is the only chance many of us have to see decent return on our collections, albeit at a very large cost of time.
Selling a gear "system" is also terrible for this reason. Nobody wants YOUR collection of gear or music. They want their OWN collection, and at best they may be interested in one of your pieces here or there. With hifi systems, at least there's maybe only a dozen or 2 components at most, and they're each a large average value, so it's definitely worth the extra effort of selling piece by piece.
Selling a gear "system" is also terrible for this reason. Nobody wants YOUR collection of gear or music. They want their OWN collection, and at best they may be interested in one of your pieces here or there. With hifi systems, at least there's maybe only a dozen or 2 components at most, and they're each a large average value, so it's definitely worth the extra effort of selling piece by piece.