I currently own a 608esd, x7esd, and a 779es, and all are very reliable. The 608 I purchased new and it has over 7000 hrs on it with no repairs and it functions flawlessly. The other two players I purchased used and the x7 had an inoperative drawer and a dirty headphone jack when received. The repairs ran about $115.00 which wasn't too bad. As far as sound quality, I prefer the x7 and the 608 over the 779. Any of these players will kill my Cambridge d500se which I purchased because it was light weight and "use of" requires it to be moved about and the Sony's are to heavy and bulky. I use the x7 as an alternate source in my main system with a Linn Karik/Numeric and yes it's not quite as good as the Linn but it does have a different sound that is still pleasing and it will play cd's that for some reason the Linn rejects. So, to answer your question, I would recommend the used Sony es players.
