[Darryl Ramm]

Stop fixating on balanced vs. unbalanced that is unlikely your issue. And the more you talk about it the more you are going to drive yourself into confused/wrong decisions or get wrong advice here.

Likely like your gear is not outputting +4dBu line level anything, balanced or not. If the output level or impedance your gear has needs a DI or preamp then use one. What gain did you use on the DI on the Omni? If you have an omni then why not use it's DI? Don't just go buying any old DI box until you understand what Gain you were using and what gain that DI offers. And you don't need to nail inputs to within a few dB, the HD IO 24 bit converters have enormous dynamic range/great S/N. You just want to be somewhat in the ball park and focused on good S/N from the analog synth outputs (and preamp/DI chain if you are using that)..