I think they are 2 very different machines if I’m honest. I was an early adapter of the DB4 and would use it purely for DJ purposes with Traktor… I had done a video back in the day showing its capabilities using MixArkitekts tsi file for mapping and it worked wonders.
Overall I was very pleased with the sound quality, although the build quality didnt feel like its earlier mixers… .(think Xone92 rotary etc).
But my advice is dont replace one with the other. They are 2 very different machines. Sure the matrix is mega cool and the studio effects are awesome on the DB4, but swapping the OT for it, you will miss out on so many other features (primarily proper sampling).
The looper on the DB4 is mega cool and its BPM detection engine is also very robust. However, having the ability to edit samples, chop them up, and then re-arrange them is invaluable. Furthermore, the sound editing features on the OT are wicked. You can completely mangle the sound, something that cannot be done with a DB4.
If you want to use it as a live DJ setup, I can understand your frustrations with the OT as it is not used in the same conventional way a proper DJ mixer is used. But you can’t sequence on a DB4 or any mixer for that matter.
Now, if you’re main concern is more ins/outs, then maybe just buy a very robust RME fireface with zillions of connections, or something similar. Personally, I use an Apollo quad and the sound quality, D/A and A/D converters are pristine. Couple that with some of UAD’s plugs and you have a very powerful setup.
My 2 cents…