I really like digitone a lot, it’s fairly unique among the other elektron offerings. There are distinct benefits to using a single device over multiple as it simplifies the process of composition and arrangement but on the downside, you are limited to what the single device offers you.
You are unlikely to find a better polyphonic synth type experience in any other elektron machine, if you enjoy using it with a keyboard the 8 voices are incredibly satisfying. Analog four is very capable and analog synthesis is really a different sonic pallette than fm synthesis but it will limit you to four voices.
Octatrack can be used with a keyboard to trigger samples and you can manipulate it into working in ways other than it was designed but it will not so easily lend itself to synthesis type sound design as any of the others which are discussed here, it will be a different experience and some people may find it tedious, I use a digitakt because I am one of those people.
Rytm as a groovebox would be great if you enjoy designing drum sounds and would also like to work with some samples, I’m not sure it will give you a rewarding experience when played as a keyboard instrument so it depends on how much of your jazz fusion focus is on the rhythmic aspects, it is less likely (but not impossible) to smoothly integrate into ambient soundscapes.
Elektron devices do pair together particularly well, and it will depend on how comfortable you are with the digitone and syntakt workflow. The common ground between rytm and analog four will be closer than digitone and rytm, similarly digitone and syntakt or digitakt will feel like a more coherent transition and therefore it comes down to what you want out of them.
Octatrack will require a sound source, and whether that be samples that you create or samples that you acquire through purchases, it will probably feel like a less musical experience. It can certainly be used musically, and in terms of arrangement and mangling sounds it will shine, but composition may feel uncomfortable coming from traditional instruments.
I don’t know how much you intend to continue using the daw or how comfortable you are leaving all keyboard/synth duties to the op1 field but that is likely something you’ll need to figure out. If you currently use overbridge or are interested in using overbridge for a hybrid workflow with your PC, the offerings in the digi boxes and syntakt might be more useful to you. If you are going to compose purely on the hardware side, I don’t think it will factor into the decision as much.
It’s hard to direct you to only one option as they are all good options, but if your tablespace and budget allows, as long as you enjoy digitone then I would encourage you to keep it, however if your interest is mostly in using the digitone midi sequencer and your op1 can handle the same duties that digitone currently does then it may be preferable to replace digitone with even a digitakt which will have 4 voices midi polyphony per midi track (8 audio, 8 midi), and can handle drum duties or take samples from op1 for arrangement.
I use digitone and digitakt together, but mostly in that I take digitone samples an add them to digitakt to arrange compositions. I’m also using and enjoying mpc live 2 which does seem to lend itself to composition and bridges some ground between polyphonic synth and sampler that elektron does not, but I personally far prefer the elektron workflow as well as the arrangement side of things. Mpc live feels more like an instrument to me though, and it has stereo sampling which digitakt does not.
Sorry I can’t be more specific for your needs but hopefully this is helpful in seeing the bigger picture of figuring out your own needs. Knowing what you’re currently missing or struggling with is really the key to finding something that works for you. Sometimes it takes 3 boxes to be happy, sometimes only one is the best course of action. It all depends on you.
