The new Eventide H90, Beebo, and of course OT can function as dual stereo Fx. So that 2 stereo synths can be used with them at the same time.
Is there any other options you know about?
Ensoniq DP/4, Kurzweil KSP8. Nord Modular G2 Engine could be used as an effects processor, 1U rack with four ins/outs, but no knobs, buttons or any other controls.
Thanks 
good ideas but I’m mostly interested in things that is a little compact as it would be for live setup.
Doesn’t have to be super small but not like a full synth size
Is that definitely correct regarding the H90, if so it’s definitely something I would be interested in. I tried to find this in the manual but couldn’t find anything ?
It can be more than one effect at a time and has 4 inputs. I understood that it is possible to have them in parallel from some product video but have not read the manual… I could have misunderstood. Latency seems like it would be a problem for me with it so I don’t think I will go for it. Not that it’s so bad but in combination with the other stuff it would become problematic.