Looking at the service manual, I don't see any difference between it and the G-8000. Perhaps all cosmetic?
120WPC for both, a PITA to work on, but solid design and serious construction. Tuner is four-gang (as opposed to the five-gang in the 9000/901), and the 8000/801 lacks the auto noise filter that the 9000/901 has. Few receivers were built as well as the G-8000/G-9000. The 9000 tends to go for about $300 or so on eBay, I'd think the 8000/801 ought to be selling for about $75 less.