They are basically identical, and both excellent players. I had my CDJ900s (also brought brand-new) about a year or so before I traded them in for teh 2900s so I’ve been able to spend a fair bit of time with both.
The SC2900 does have hot-cues, seperate start/stop time adjust, jog-wheel torque adjust, and a BPM master sync type thing (similar to the 2000nexus I believe) in addition to all of the CDJ900s features.
It also has (in my opinion) a noticably superior jog-wheel, in fact I’d say it’s the best jog-wheel I’ve used. It is butter-smooth and doesn’t feel at all mechanical, and the different torque settings are each sufficiently different to be useful.
The pitch slider I felt is marginally better on the CDJ900 (I just prefer the feel of them) but after a couple of weeks with the 2900 I’d almost forgotten this.
The SC2900 is also noticably heavier than the 900 and feels somewhat more solid. I doubt there is any real difference in build quality between them, and neither feel anywhere near the old CDJ1000 in terms of weight/cost ratio (a ratio I may have just made up), but the 2900s hard casing and extra weight is noticable over the 900.
The screens are comparable- the 900s is slightly bigger but this extra space is just used to display an extra line of text (useful when using the player’s screens to browse music -see below- and to space things out a bit) and the waveforms are pretty much identical on both.
I don’t use my 2900s with an iPad (Apple products just arn’t my thing), but I do use them via D-Link connected to a network switch, and then into a small 10" netbook running Engine software. This way the tiny netbook is just used to the side as a music browsing screen (controlled 100% via the 2900 onboard controls so no need to touch the netbook) as I’ve never been a fan of using a laptop when DJing.
For me the Engine software does have a slight edge over Rekordbox (and I am a big fan of RB)- I find Engine much more intuitive when using it simply as a linked record crate, and I’ve had zero stability issues when linked to the players unlike Rekordbox with my 900s.
So overall they are very similar- (and indeed anyone who has used any full sized Pio-CDJ could play on an SC2900 blind-folded, they are laid out & function exactly the same) but for me the 2900 has the edge over the 900, particularly in terms of the extra features and the excellent jog-wheel, in this sense it sits somewhere between the CDJ900 & CDJ2000mk1. The fact it costs less than a CDJ850 is remarkable and does make you realise how much you have to pay simply for the Pioneer name.
That said, I would still swap these in for the CDJ2000nexus in a heartbeat given the funds, but I would happily recommend the SC2900 over a CDJ900 all day long unless the user is regurlarly playing in Rekordbox-player-equipped venues. The CDJ850 for me is a complete white elephant at it’s current price- not even having D-Link or Quantize (vastly improving the use of the auto-looper) and costing more than the SC2900.
For me: CDJ900 < SC900 < CDJ2000. For me the 850 is so far behind these three that unless a pair were available for an absolute bargain of a second-hand price they wouldn’t get considered.
Think that covers most of it Makar! Apologies for the slight thread divergence, hopefully some might find some of that useful though 