It’s hard to say, and it depends on how the Content is wired. Some organ onboard mixers do feed all amplifiers from the external inputs, but not all do. In either case, it’s a common complaint that on board organ sounds being fed from Hauptwerk don’t sound as good as you expect. I don’t think it’s worth your time to modify the Content, the 8 channels and 13 drivers are probably being driven with some redundancy, and the mixer is probably acting as a glorified crossover. So technically it’s just a sophisticated 1 or 2 channel instrument with lots of drivers in the mid and high range, and the signal divided among them. That’s part of the reason why it’s hard to get good results from using the instrument’s aux in. The most useful part is probably the Sub.
So my advice would be to ditch the Content’s internals and go for a good external system.