Ohh....divided loyalties here... I love both units - the Gemini which I reviewed was really good... nice selection of features, great outer finish, and deep blue displays to stare into for hours...glowing...glowing...hmmmmmmm
Huh?

Where was I, oh yeah.... you could buy the Gemini MP-3000x and you wouldnt regret it - great deck. As my review said...forget everything that old, long-in-the-tooth, DJ equipment retailers (and/or DJ's) might tell you about how Gemini equipment USED TO BE ... Gemini have moved on, and up.
A full feature run-down on the Denon DN-D4000, does bring several important features into play however, and one stunningly clever, useful, all-be-it a little boring feature too.
Heres the list: (cut'n'pasted shamelessly from Denon.com website.
• Worlds First Double CD/MP3 Player with ID3 Tag & CD TEXT Display
• MP3 playback, supports V.B.R. & C.B.R.
• ID3 Tag support for MP3's; Artist, Album & Title (worlds first)
• .m3u Play list compatible (worlds first)
• CD TEXT Support
• Folder/File search
• Plays CD-R/RW media
• 2 Seamless loops per track or disc
• 2 Hot Starts & Stutter Cue points
• Brake Effect
• Relay Play, Program Play, Repeat Play, Power on Play
• 2-way Pitch Bend -by Jog Wheel & buttons
• Auto Cue to music
• Instant start
• 10 sec CD /100 sec MP3 Shock Proof Memory
• Jog/Shuttle Wheel (50mm)
• 1 min skip search in either direction
• Rotary track selector knob
• Illuminated action buttons w/ tactile feedback
• Illuminated drive trays
• Auto close disc tray system
• Sleep mode -prolongs the useful life of internal parts
• Fluorescent tube display (segment + dot matrix)
• 4 way time display -track or disc elapse/remain
• Pitch range ± 4%, 10%, 16%
• User adjustable presets
• Custom Memory -save up to 600 Loops and Cue's internally
• User adjustable presets
• Firmware upgradeable by CD-ROM disc and it's FREE!
• Digital Output (SPDIF)
• Fader Start
• 2RU controller and transport
• Black 8-pin 10 foot remote cable supplied
• Gray 8-pin 16 foot remote cable is available through parts - part number 2042656009
Drink your coffee, its probably gone cold by now....
Whats the boring, but very useful feature? Well, its the "Folder/file" search system. This feature is not mentioned in the leaflets, nor the Denon PLASA glossy DJ booklets, nor known about by many average DJ stores. Why? Well, this feature wasn't on the original models of 4000 when they left the factory. However, like all Denon's current kit, the software/firmware inside the 4000, is user loadable :- Denon release a new version of the software, you download it off of their website onto a CD-R(w), load the CD into your Denon CD-deck, hold down a couple of buttons and "PING!" 2 minutes later you've got the latest version of the latest Denon Dn-D4000 - just as if you'd bought it that day.
Folder/file search...ah yes... OK, MP3 CD's can, of course hold over 200 tracks...thats far too many to print onto the CD-label, or even in the front cover, back cover and inside covers of a CD-case. So...the options are... Carry a ringbinder folder with you to every gig, with each CD's track listing covering 2 sides of A$ for every disc, or...The Denon way.
The Folder/File search system allows you to display every single track on your MP3 CD, in alphabetical order by Artist Name, or Song Title, or folder name. Good eh?
Now On the 5000 and 3000, you can do that search/sort even whilst the current track is playing, I've not tried that (yet) on the 4000. However, I can find out for you tomorrow...oh...look at the time...Today, I mean...