My oldest piece of equipment is an ARC SP9 mkII preamp. Perhaps not the best ARC as done, but certainly not the worst. A few years back I listened to the LS25 thinking it might be time to upgrade. While I felt it was a definite improvement, it also had a high price tag. As I was looking at alternatives, I stumbled on Steve Huntley at Great Northern Sound who does mods on much of the ARC gear. After much discussion with Steve, I had him apply his reference mod on my SP9 and have to say the results were simply remarkable.
Steve knows ARC gear inside out (he used to work for them) and if there's a particular piece you're interested in, I'd definitely give him a call... www.greatnorthernsound.com