Oh boy, it's been awhile. I'll dig out the specs. In the meantime, the 7000 and 3900 use rs-232 connections, the 7000 is about 2 inches tall and 4 inches wide while the 3900 is about DIN size. Also, the 7000 is much faster but the 3900 can have multiple screens if set up. That's off the top of my head. I've deinstalled the 7000 and switched to a din size Kenwood touch screen which I'll use with Jules new program so I don't have photos. Right now there is no program available to interface the Empeg but V99 was working on one which he was planning on releasing when all 3 screens were ready to go.