Gain staging can be a little bit of a point of confusion when nothing seems to be audibly clipping. The ideal way would be to use your DAW or other method of accurately measuring output and use a test tone to set a consistent level between the 2 peripheral devices on their own volume pots, then input that into the DT and control mix volume from the DT as the master mixer. If you don’t have a way to measure volume, you could either wing it and try to determine a similar level using the parts you’ve already played, you could create a test tone of comparable pitch and timbre and play it with each again using your ears to calibrate, or you could leave it as is and do all mixing from the DT mixer.
If you leave it to the DT mixer exclusively, you will potentially run into problems later if you run out of room before you redline. Generally even digital equipment will sound different the closer it gets to redline because it’s driving the opamps harder. If you want consistency of sound, try and volume match them beforehand using one of the standard methods or devise your own. Either way, the impact on your final recording should be the same if you leave enough headroom to adjust and later mix to taste.
If you want you can search here or on google for “gain staging” and there are lots of people who can say it better or more completely than I can, but that’s the basic concepts as far as I can convey them.
One disadvantage to the left/right method that you’re using is you lose any stereo data coming out of the DN and minilogue, you might want to consider a small stereo mixer or routing the minilogue through the DN and then sending the L/R of both through the DT and just use the small mixer (moukey or other if you can afford a better one) for leveling before the DT mix.
To me, that would be a more ideal usage unless you are only running audio into the DT to sample those other devices, because in that case it won’t matter either way (being that DT sums to mono regardless). I’m sure there’s more ways to do it but that’s what I’m thinking at least. Anyways welcome to the forum and good luck.