Reply to recommendations for midi controller for my set up/situation

Hi all,
A bit of background
1) I am an idiot
2) I have Traktor 2.5 registered version
3) I have macbook pro 15" 8GB Ram
4)I have Roland sp-555 sampler/drum machine
5)cheap (and nasty) Behringer BCD 3000

OK so I have a bit of gear and play around with traktor for years- I was a teacher and using dj gear with kids so in that situation I had access to a vestax vci-100 (which was great but I found it hard to scratch)
Now I am not a teacher anymore but a digital developer (3D animation, special effects, film editing etc)
part of this etc is music production (low rent- basically bedroom dj/producer)

So, apart from the bcd-3000 my gear is pretty good, I am looking to get a midi controller that I can use for my current situation but which also at a stretch could play a live gig. I am very interested in scratching, but I don't know much about it, so will never become a turntablist..... but it is high on my list of things to do with a new midi controller...
So S4? Better for scratching, but I already own traktor 2.5 so wasted money
or VCI-400? better built, more customisable, but I really want the better S4 jog performance

And also with either of the above 2 controllers can I mod/map/hack my roland sp-555 to trigger the remix decks?
I only can map the top 4 slots at the moment- will it be possible to do more in the future?

I am getting old guys (turned 40 this year so basically dead) so I only have one shot at buying a $900 controller..
What are your thoughts..
Cheers
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