If you already have an audio interface with Adat then it’s the ES-8 for you, otherwise ES-9, which a lot of people are craving right now.
If you only need MIDI out from your computer, and audio in to the computer, then you don’t really need Expert Sleepers. What the ES-* modules allow is to send both audio and CV, both from computer to hardware and from hardware to computer. This allows for building an extremely flexible and cost-effective hybrid software+hardware system, plus a DC coupled audio interface (like the ES-8/9) is by far the superior way to sync sequencers and clocks between computer and hardware, if you need that. Watch that Loopop video above, that should give you a good eyeopener on this subject.