Hey!
I remember I had v4.0c on my SD1 Plus, and the same OS is working on SD1 classic.The nice point is that you may use the sampler for different tasks.I even use it for backup voices...!Or live guitar riffs..it sounds great!
I loved SD1+ the only reason I don't have it anymore is the weight, almost 35 kilos with flight case..so I turn to Midjay.
Vio