You are correct about the channels wrapping around, so channels 5,6,7,8 are just like 1,2,3,4. I have an alternative firmware version that does not do this. The Synthino listens for 1,2,3,4 and also the drum channel 10. Would this be helpful? Can you make your other synths listen on channels above 4?
I do this you would need to load new firmware onto the device. It is not that hard, but if you are not technical, it could be tricky for you (some people find it too difficult I guess).
If you only want it to listen on channel 1, just say the word and I can make a version that does that. But you’d have to load it according to the Windows or Mac instructions above. Just let me know.