#1: a live looper -> If you mean 'real-time' live looper, then no not really, because there will be a pause between grabbing and saving such a captured loop. Not to mention you can only 'loop capture 15 seconds', although you can use 'sampling' instead for longer loops/recordings. Still, same goes for that, there will still be a pause between capturing the loop and saving. The loop capture will be on the 'play' pad near-instantly but you can't use effects on the captured loop unless you save it to a pad. (at least I don't know how). Remember though that if you use a good mixer, you could theoretically grab a loop in real-time, save it when the SP-555 isn't used for playback and then at a later time throw it live back into playback.
#2: when this grabbed sounds are looping, I want to perform / liveremix
them with filters, maybe pitch, rearranging it live -> Although it is possible to use effects on grabbed loops, as far as I know it's only possible when you first save the grabbed loop to a pad, which again causes a pause.
#3: -> No idea, but I think it will.
#4: Is it possible to "dump" these mixes into the 555 and use the machine as i use my CD-Player ?
Yes, you can store entire songs as samples and play them back, just make sure you've got enough space on the compact flash card and don't go over 160 files in total or so (can't quite remember the limit, but has to do with pads and banks with which you trigger them).
#5 If YES
How fast is it to load these mixes from the card ? -> Near instantly if not totally instantly. I have yet to come across a sample that had to load before I could play them back from the sp-555.
ex: I load 1 looping hornsample from the card and makes it play
then I remember that a special string-sample will fit well
Is it possible to load that string sample into another pad without stopping or do i have to prepare all the pads as a bank ?
-> You'd have to prepare, because again any recording or loading into a pad would need a pause to save to a pad, but when the sounds are already on the SP 555, you can switch banks without stopping the playback of the looping sample through using the 'hold' function when doing a live performance, but you can also sequence them into a 'pattern'.
The best use of the SP 555 for live performance in my opinion would be to do live effects on in coming sound, so you're using the SP-555 as effects processor, not so much as a sampler. The sampler stuff is awesome, but you'd have to prepare that, unless you're going to use mixers and different sound sources in between that would give you enough time to make something on the fly and live. Another good solution would be to save songs you want to do some effects on as samples onto the sp-555 and then trigger them with the pads..
#6: Sorry, I don't own a RS7000.
Hope this gave you enough information. I have to add a little disclaimer though, because I have got my sp-555 only a few weeks now, so there might be plenty of things I do not know about.
Cheers,