The CD51 came out around 1991. Earliest version of it had a wire basket cd magazine (would require updated molded magazine kit). Also had a CDM4 player (would require a CDPRO player upgrade kit, about $800 to buy). Equipped with a Rowe "OBA" bill acceptor (requires an update chip to be installed in the OBA control box to take the latest currency). Has an amplifier of 250 watts capacity, but only has a 3 band graphic equalizer built in. Title pages are four disks high and different than the CD100E.
The CD100E came out around 1995. Probably had a CDM12 player installed, but a CDPRO or CDPRO2 player is a drop in plug 'n play replacement (about $400 to buy if needed). Equipped with a 250 watt amplifier with a 7 band graphic equalizer (amplifier interchangeable with all previous cd100 series models). Has a Rowe RBA7 bill acceptor installed (obsolete, not updateable, must be replaced with a Mars upgrade kit to acceptor modern currency, about $400 for the kit).
A tavern about 90 miles from me has had a CD51 installed and operating since it was brand new and out of the crate. Over the years I have rebuilt the bill acceptor twice (completely re-belted, cleaned, and updated), replaced the cd player twice, replaced several broken title pages, and replaced several burned out fluorescent tubes. It's a heavy use machine and has been fairly reliable. One thing the owner did was to bypass the original amplifier completely because he has live bands on Friday and Saturday nights. The RCA audio output jacks on the Mechanism Control board in the jukebox feed via cables over to his audio mixing board behind the bar. The bands also patch their audio signals in there since the mixer feeds out to the tavern's own speakers located throughout the building. The bartender just fades down the jukebox fader on the mixer and fades in the band fader on the mixer. The tavern owner likes this jukebox because it is so small. He pays me good to travel to fix it when needed.