Having owned the S2400 and the SP-1200 for some time now, I can confirm, that they sound very different (as opposed to what Brad mentioned in some of the videos discussing the input/output circuitry being identical) and I’m glad I kept the SP-1200 and probably will never sell it. It makes samples sound amazing (esp. drums) by adding a certain fatness and weight coupled with a tightness that is not present in the S2400.
I probably should have been more skeptical before buying the Isla S2400… seeing how exacting Dave Rossum was in his design and engineering process and the pains he went through to get identical (or as-close-to) circuitry for his current SP-1200’s (this page says it all: FAQ – Rossum Electro-Music). A job like this is not easily replicated and there’s a reason why Rossum is considered a genius and a legend - being thorough is part of that.
I’m bummed to find out that the implementation of the Isla S2400 analog filters feel like they’re an afterthought, sonically speaking. They’re a core part of the original SP1200 sound and even if the same chips were used, if they’re not calibrated properly, they can result in very different sound, which is the case here. There maybe some use cases for them, but they sound nothing like the SP1200 with which all the analog filters are useful and help the machine have that legendary/magical sound we all know and love. I know everyone says stop comparing the two machines, but Brad himself said the filter circuitry was identical in multiple videos.
That said, I see the S2400 as covering duties in my production workflow in the territory of “general stereo vintage sampler” along the lines of an MPC or equivalent so it has its uses (even if I felt a bit misled in the marketing/explainer videos from Isla about how close it would sound/circuitry to an SP-1200). The modern workflow in it is great, and by no means does it sound bad - it sounds good and shouldn’t be compared sonically to an SP1200 though it originally was drawing those comparisons by Isla instruments themselves. That said, I’m currently on the fence about whether to keep the S2400 or just replace it with a classic MPC. If I keep it, its mostly for its modern workflow over the classic MPC workflow/slower OS,etc.