Something like an LM3886 would provide plenty of power and sound quality for your needs. I'm obviously partial to my
LM3886DR, but there are many other incarnations of the LM3886, including a
free layout should you want an all-DIY route. If you choose the DIY route, I recommend that you read my
Taming the LM3886 article series.
Can the organ software handle crossover duty as well? If so, you can implement the crossover digitally. That'll save you a bunch of trouble. The drawback is that you'll then need three DAC channels and three amplifiers.
Tom
