I'm sure Stan will know exactly what you mean, as would a few electronics bods, but remember Leo that you are in a distinct minority of audiophiles and hi-fi enthusiasts. I would class myself as a complete digital head with a basic working knowledge of electronics, but I still wouldn't dream of opening a DAC to make alterations to the circuitry. I'd say that most customers of Stan's would be the type who want excellent quality from a box that has plenty of connectivity and works well. Four inputs is plenty for most folk, heck most DACs only have one or two, and those who want USB can choose the 7520, those who don't may opt for the 7510 - either was they're on to a winner. If the desire to get the best one is there then they will choose the 7520.