S1000 and s1100s read S900 format disks. On a whim I loaded the same akai disk into the 900 and the 1100. The 900 cracked, and was clearly better sounding than the 1100, same disk. The one you showed had the original factory disk drive. Looks like the factory disk set as well. You can get some of the software features on the 950 into the s900 which has lessd memory than the 950, but here is the kicker, you need to load a boot disk to get them, no eprom (why no eprom upgrade!!? Why ?!) and to keep it interesting boot disks now can only be copied using an atari and and a software program. I have it but had to borrow an atari to make the disk, no atari now. My advice is see if you need it after you get your 2400. If it still has the crunch you want then go s900 audio out into the 2400. Years ago friends thought I was nuts to talk about collecting vintage samplers but there is a hell of alot of fine circuitry in there and it is part of tone for me. If you have an issue with your S900 drive and you want to stick to the drive (not a samplerzone kit top replace it) PM me as I used to have files on which chinon drive works and what the jumper settings are.
Appreciated dude cheers.
Im still in two minds what I’m gonna do with it, Very tempted to not touch the thing and try hold on to it for a good price. Then again, I can’t see that actually happening 
If I am gonna use it I’m going to to try stay away from the floppy disk side of things.
As far as i am aware you can still get all the goodness out of it by just sampling the processed audio directly into directly into the s2400 right? Would much rather do it that way, have in the s2400 and save to sd card