acalex said:1) will the SBT be up to the job?
You already have these ... how does it sound to you and can you live with it for a while?
acalex said:2) Will the sound improve drastically IF i swap the SBT with a more expensive stremer (say for example the Linn Sneaky or the Majik DS)?
Most people would say yes if your system is resolving enough, and it sounds as though your almost chosen system will be. But since you are using a valve amp then a very high resolution digital source might not be as important .. just a good one will do e.g. Majik DS(M).
acalex said:3)...having an high-end DAC (let's say Jadis, 4k eur) and a Sneaky DS (1k) I will end up same price as a second hand Klimax DS or a new Akurate. Will this combo be better than the Linn all-in-one solution?
4K on a DAC!!!?!?!? I would question what going over 1K on a DAC brings you in terms of sonic ability, or are you paying for the casework and low volume exclusivity/hand-made components. Have a look at North Star (an Italian company
4)Will I need, in the future, to upgrade my digital source if new technology comes out?
If a digital source at least copes with 24/96 then you should be OK for a few years ... after all CDs have been around for 25 years. I think future proofing for 192/24 or higher resolutions might make a little bit of sense sense but you might be paying extra for technology that you may never use or cheaper next year, and the availability of music at this resolution is both limited and very expensive. And why spend so much when you love the turntable as a source more.