I made a DIY patchbay with cables soldered directly to sockets and plugged into my synths. I then soldered cables to the switching (normalling) contacts on the sockets and plugged those into my mixer.
This way I have an uninterrupted signal going into the mixer, but if I want to "insert" an effect it is easily accessible and breaks the normalled connection. The returns go into more sockets on the patchbay.
But what about a stereo instrument (Voyager, Andromeda) going into a mono effect?
To accomplish this I added an extra DPDT switch, which provides a stereo signal on one throw and a passively mixed (2x 10k resistors) on the other. You do get 4 dB attenuation, but this can be compensated for on the effect or the instrument's master volume.