Routing to external Midi Instrument problem/bug?

I am using Dorico for composing, in this case for string orchestra… I don’t want my playback to be the string sounds because if I have written fast passages the soft envelopes mean the notes do not sound before they are gone (if you know what I mean!) and it is very hard to check for wrong notes. Changing to another software instrument also not what i want because I don’t have a sound system hooked up to my Mac Mini.
Instead I simply want the output to go to my attached Casio keyboard (and come out as piano). So I set the output of all instruments in the Inspector to my midi keyboard, channel 1.
Then I run into the following bug: When I write music into the 1st violin part, it will play back on the Casio as expected. But when I then write into the 2nd violin, only the 1st violin part is played back. I can fix it by then setting the 2nd violin to Channel 2, then back to channel 1… .then it works.
Quite strange and I have not been able to find a solution to setting all instruments to one channel permanently.
Any ideas?

MIDI has an Omni setting. I wonder whether that would help, either at the Dorico end or the Casio end.

I don’t think so-- I just want Dorico to transmit to a single midi channel (as if it were a single instrument with multiple lines).
But it is possible that I have misunderstood some principles…

Can you attach a simple, minimal project that demonstrates the way you have the routing set up in the track inspector in Play mode, so I can take a look?

Daniel, here is a simple example. A string orchestra, but I want all parts to play back as piano on my external keyboard as I am composing.
I routed all the outputs to the midi keyboard, and they play as expected. But then I try changing the output to channel 1 on more than one track (in this case I have just changed violins 1 and 2, but ideally I want all to output to the piano sound) and the playback – which, curiously, works on the first run-- only plays one of the tracks if any changes are made to the score.
Or is there a setting to allow more than one track to share a channel?
Or do I need to send a program change message as an init to the keyboard?
test ext midi kb.dorico (1.8 MB)

You’re using quite an old version of Dorico 4, Geoffrey. I recommend you update to version 4.3.30, and I think you will find this works as you expect.

Will do! I was using my old machine for the first time in a while, and have not updated.
Thanks for your infinite patience.