As a stand-alone unit, it seems to be missing a filter and a dedicated LFO.
The ES8 gives you DAW to CV access. That means your DAW will have to generate gates and CV. The other solution is to use a MIDI-to-CV solution. The FH2 can do this. There are also much more simple modules that are smaller in space with the same functionality as an FH2, but more limited in scope.
For me, I'd ditch the ES8 and Optomix. That opens up 16HP.
I'd put in a 2HP LFO v2 (2HP) and a Befaco MIDI Thing (6HP).
I'd also put in a Happy Nerding HN VCF (6HP) and a 2HP Mix (2HP).
Those changes will give you a lot more options in your rig.
You can open up 4 more HP by ditching the York quad attenuator and using external attenuators in line with your patch cables. Koma makes patch cable extenders that do just that. You can then use that 4HP for something like an Expert Sleepers Disting Mk4. That will give you a boatload of extra functionality to experiment with.
This is just one possibility and you might be able to swap other modules if they are to your liking.